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FLUORESCENCE  OF  THE  URANYL  SALTS 


BY 
EDWARD  L.  NICHOLS  and  HORACE  L.  HOWES 

IN   COLLABORATION  WITH 

ERNEST  MERRITT,  D.  T.  WILBER,  and  FRANCES  G.  WICK 


Published  by  the  Carnegie  Institution  of  Washington 
Washington,  1919 


LIBRARY 

UNIVERSITY  OF  CALIFORIJIA 
DAVIS 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  298 


PRESS  or   GIBSON  BROTHERS,  INC. 
WASHINGTON,  D.  C. 


CONTENTS. 


PAGE 

I.  Historical  Introduction 5 

II.  The  Structure  of  Fluorescence  Spectra 10 

III.  Preliminary  Observations  on  Certain  Uranyl  Salts 15 

IV.  Phosphorescence  of  the  Uranyl  Salts 38 

V.  Intimate  Structure  on  Cooling  to  -185°  C 61 

VI.  Polarized  Spectra  of  Double  Chlorides 102 

VII.  The  Nitrates  and  Phosphates;  Water  of  Crystallization;  Crystal  Form 122 

VIII.  The  Acetates 146 

IX.  The  Sulphates 169 

X.  Frozen  Solutions 180 

Appendix  1.   Chemistry  and  Crystallography  of  the  Uranyl  Salts 207 

Appendix  2.   On  Phosphoroscopes 231 

3 


PREFACE. 


This  volume,  the  completion  of  which  has  been  much  delayed  by  the 
participation  of  America  in  the  World  War,  contains  the  results  of  an 
investigation  covering  a  period  of  eight  years.  The  discovery  by 
Becquerel  and  Onnes,  that  the  fluorescence  of  certain  uranyl  compounds 
is  resolved  into  groups  of  narrow  line-like  bands  when  these  substances 
are  excited  to  luminescence  at  very  low  temperatures,  suggested  to  the 
present  authors  the  desirabiUty  of  a  thorough  and  systematic  study  of 
this  subject. 

The  spectra  of  numerous  uranyl  salts,  many  of  which  were  espe- 
cially prepared  for  this  purpose,  have  now  been  mapped.  Owing  to 
the  extraordinarily  complex  character  of  the  phenomena,  no  satis- 
factory theory  has  as  yet  been  evolved,  but  the  mass  of  facts  here 
recorded  and  the  general  principles  established  will,  it  is  hoped,  afford 
a  basis  for  the  successful  theoretical  development  of  this  important 
and  nttle  understood  branch  of  the  science  of  radiation. 

Physical  Laboratory  of  Cornell  University, 

May  24y  1919.  • 


FLUORESCENCE  OF  THE  URANYL  SALTS. 


By  Edward  L.  Nichols  and  Horace  L.  Howes. 


I.  HISTORICAL  INTRODUCTION. 

The  beginnings  of  precise  knowledge  concerning  the  luminescence  of 
the  compounds  of  uranium  are  to  be  found  in  the  classical  memoirs 
of  George  Gabriel  Stokes  and  of  Alexandre  Edmond  Becquerel.  It  is 
true  that  Brewster^,  who  observed  the  fluorescence  of  chlorophyl  and 
other  substances  in  1833  and  gave  the  phenomenon  the  name  of  internal 
dispersion  J  mentioned  a  yellow  glass,  doubtless  the  ''canary  glass"  of 
commerce,  which  exhibited  the  same  property,  but  it  remained  for 
Stokes,^  by  means  of  the  beautiful  experiments  described  in  his  papers 
entitled  ''The  Change  in  the  Refrangibility  of  Light,"  to  really  eluci- 
date the  phenomena  and  to  lay  the  foundation  for  all  subsequent  work 
on  fluorescence. 

Having  observed,  by  the  use  of  suitable  light-filters  and  by  his 
ingenious  and  elegant  method  of  transverse  dispersion,  the  unusual 
character  of  the  fluorescence  and  absorption  of  this  glass,  Stokes  pro- 
ceeded to  the  investigation  of  such  compounds  of  uranium  as  he  was 
able  to  procure.  From  the  nitrate  he  made  the  acetate,  oxalate,  and 
phosphate;  also  uranates  of  potassium  and  calcium  and  the  oxides. 
He  also  obtained  specimens  of  autunite  (uranyl  calcium  phosphate) 
and  chalcolite  (uranyl  copper  phosphate).  After  observations  of  these 
minerals  he  writes  (Sec.  145) : 

"The  intervals  between  the  absorption  bands  of  green  uranite  were  nearly 
equal  to  the  intervals  between  the  bright  bands  of  which  the  derived  spectrum 
(1  e.,  the  fluorescence  spectrum)  consisted  in  the  case  of  yellow  uranite.  After 
.  having  seen  both  systems  I  could  not  fail  to  he  impressed  with  the  conviction  of  a 
most  intimate  connection  between  the  causes  of  the  two  phenomena;  unconnected 
as  at  first  sight  they  might  appear.  The  more  I  examined  the  compounds  of 
uranium,  the  more  this  conviction  was  strengthened  in  my  mind." 

Upon  reading  Stokes's  memoir  one  can  not  but  feel  that  had  he  had 
at  his  command  a  modern  specti'oscope  he  would  infallibly  have  antici- 
pated by  more  than  half  a  century  much  of  the  recent  work  on  fluores- 
cence. He  used  light-filters  to  prevent  the  exciting  beam  from  sub- 
merging the  fluorescence  on  the  one  hand  and  to  exclude  the  exciting 

1  Sir  David  Brewster,  Trans.  Roy.  Soc.  Edin.,  vol.  xii.     1833. 
«  Stokes,  Phil.  Trans.,  1852,  p.  463;  1853,  p.  385. 


6  FLUORESCENCE    OF   THE    URANYL   SALTS. 

rays  from  entering  the  eye  on  the  other,  and  thus  by  means  of  a  prism 
held  to  the  eye  was  able  to  observe  the  spectra  of  both  fluorescence  and 
absorption  with  surprising  accuracy. 

Paragraph  148  of  his  paper  describes  his  observations  on  uranyl 
nitrate.  In  the  following  quotation  of  that  paragraph  certain  pas- 
sages forecast  in  an  extraordinary  manner  some  of  the  conclusions 
reached  in  subsequent  chapters  of  the  present  monograph: 

"The  sun's  light  was  reflected  horizontally  by  a  mirror  and  condensed  by 
passing  through  a  large  lens.  It  was  then  transmitted  through  a  vessel  with 
parallel  sides  containing  a  moderately  strong  ammoniacal  solution  of  a  salt 
of  copper.  The  strength  of  the  solution  and  the  length  of  the  path  of  the 
light  within  it  were  such  as  to  allow  of  the  transmission  of  a  little  green  besides 
the  blue  and  violet. 

*'A  crystal  of  nitrate  of  uranium  was  then  attached  to  a  narrow  slit  and 
placed  in  the  blue  beam  which  had  been  transmitted  through  the  solution, 
the  crystal  being  turned  toward  the  incident  light.  The  hght  coming  from 
the  crystal  through  the  slit  was  then  viewed  from  behind  and  analyzed  by  a 
prism.  A  most  remarkable  spectrum  was  then  exhibited,  consisting  from  end 
to  end  of  nothing  but  bands  arranged  at  regular  intervals.  The  interval 
between  consecutive  bands  appeared  to  increase  gradually  from  the  red  to  the 
violet,  just  as  is  the  case  with  bands  of  interference.  Although  this  interval 
appeared  to  alter  continuously  from  one  end  of  the  spectrum  to  the  other, 
the  entire  system  of  bands  was  made  up  of  two  distinct  systems,  different  in 
appearance  and  very  different  in  nature.  The  less  refrangible  part  of  the 
spectrum,  where,  only  for  the  crystal,  there  would  have  been  nothing  but 
darkness,  was  filled  with  narrow  bright  bands  due  to  the  light  that  had  changed 
its  refrangibility.  The  more  refrangible  part  of  the  spectrum  was  occupied 
by  the  system  of  bands  of  absorption.  The  interval  between  the  most  refrang- 
ible light  band  and  the  least  refrangible  dark  band  of  absorption  appeared  to 
be  a  very  little  greater  than  one  band  interval,  so  that  had  there  been  one 
more  band  of  either  kind  the  least  refrangible  absorption  band  would  have 
been  situated  immediately  above  the  most  refrangible  bright  band.  With 
strong  light  I  think  I  have  seen  an  additional  band  of  this  nature." 

Becquerel,  in  the  course  of  his  work  on  phosphorescence,  notes  the 
fact  that  most  of  the  compounds  of  uranium  show  a  strong  emission 
of  Ught  when  examined  with  the  phosphoroscope.  He  determined 
the  duration  as  three  to  four  thousandths  of  a  second;  and  to  test  his 
empirical  formulae  made  measurements  of  the  rate  of  decay  which,  as 
will  be  seen,  are  in  good  agreement  with  the  results  described  in 
Chapter  IV  of  the  present  treatise.  With  a  prism  of  carbon  bisulphide 
he  observed  8  bright  bands  in  the  spectrum  of  the  phosphorescent  light 
of  uranyl  nitrate;  he  determined  the  approximate  range  in  the  violet 
and  ultra-violet  of  the  exciting  rays;  noted  that  the  bands  in  the 
spectra  of  various  uranyl  salts,  such  as  the  chloride,  fluoride,  and 
uranyl  potassium  sulphate,  occupy  different  places.  He  also  esti- 
mated their  relative  displacements  when  compared  with  the  bands  of 
the  nitrate.     By  comparing  the  spectrum  of  the  nitrate  during  excita- 


HISTORICAL.  7 

tion  with  that  of  the  afterglow,  Becquerel  reached  the  very  important 
conclusion  that  the  fluorescence  and  phosphorescence  are  identical. 
This  point  finds  ample  confirmation  in  the  present  work. 

In  1872,  E.  Becquerel  returned  to  the  study  of  the  uranyl  salts. 
The  following  are  the  conclusions  reached  in  this  investigation:^ 

(1)  The  salts  of  the  protoxide  of  uranium  are  inactive. 

(2)  Many,  but  not  all,  salts  of  the  sesquioxide  (uranyl  salts)  are  active. 

(3)  Five,  six,  and  sometimes  seven  bright  bands,  or  groups,  are  visible; 

lying  between  the  Fraunhofer  lines  C  and  F. 

(4)  The  positions  of  the  bands  vary  for  different  salts,  but  are  always 

the  same  for  a  given  salt. 

(5)  The  acid  of  composition  determines  the  disposition  of  both  bright 

and  dark  bands. 

(6)  In  double  salts  of  the  same  acid  the  composition  of  individual  groups  is 

the  same,  but  their  position  is  not  the  same  for  the  different  salts. 

(7)  In  a  given  substance  the  distance  between  bands,  as  viewed  in  the 

spectroscope,  increases  from  red  to  violet;  but  the  differences  of 
wave-length  decrease.  The  ratio  of  the  above  distances  to  the 
square  of  the  mean  wave-length  is  nearly  constant  throughout  the 
spectrum,  and  this  ratio  (d/2)  is  the  same  for  the  various  salts. 

(8)  No  simple  relation  is  apparent  between  the  location  of  homologous 

bands  in  different  compounds  and  tjie  chemical  properties  of  the 
compounds. 

(9)  The  absorption  spectra  also  differ  for  the  various  compounds  and  the 

absorption  bands  seem  to  form  a  continuation  of  the  fluorescence 
series. 

(10)  The  location  and  character  of  these  spectra  being  fixed  and  definite 

for  each  compound,  we  have  the  basis  for  an  analytical  method 
similar  to  but  less  general  than  ordinary  spectrum  analysis. 

In  1873,  Henry  Morton  and  H.  Carrington  Bolton  published  an 
account  of  extended  studies  of  the  fluorescence  and  absorption  of  the 
uranyl  salts.^  Their  list  contains  85  substances,  chiefly  of  iheir  own 
preparation,  including  17  double  acetates;  but  not  all  of  these  com- 
pounds were  found  to  be  fluorescent.  Readings  were  made  on  the 
Bunsen  scale  in  vogue  at  that  time,  and  some  of  these,  for  comparison 
with  our  own  determinations,  will  be  found,  reduced  to  approximate 
wave-lengths,  in  Chapter  III. 

Figure  1,  which  is  reproduced  from  the  paper  of  Morton  and  Bolton, 
gives  an  excellent  general  view  of  some  of  the  most  interesting  of  their 
observations.  The  unshaded  portions  are  fluorescence  bands,  the 
shaded  regions  are  the  bands  of  absorption.  The  partial  resolution 
of  the  bands  in  several  cases  is  clearly  shown  and  the  breaking-up  into 
distinct  groups  of  the  uranyl  ammonium  chloride;  also  the  coincidence 
in  certain  cases  of  absorption  and  fluorescence  in  what  in  this  mono- 
graph we  shall  term  the  reversing  region. 

^  E.  Becquerel,  Comptes  Rendus,  lxxv,  p.  296.     1872. 

2  Morton  and  Bolton,  Chem.  News,  pp.  47,  113,  164,  273,  244,  257,  268.     1873. 


8 


FLUORESCENCE   OF   THE   URANYL   SALTS. 


The  authors  note  specifically  the  following  further  important  char- 
acteristics of  the  spectra  of  the  uranyl  salts: 

(1)  The  steeper  gradation  of  light  on  the  side  toward  the  violet  in  the 

case  of  bands  showing  a  single  crest. 

(2)  The  weakness  of  the  outer  bands,  both  toward  red  and  violet,  com- 

pared with  the  central  bands  of  the  spectinim. 

(3)  The  overlap  of  fluorescence  and  absorption. 

(4)  The  systematic  shift  of  bands  when  a  salt  is  dissolved  in  water  and 

other  solvents. 

(5)  The  remarkable  changes  due  to  the  dehydration  of  salts  containing 

water  of  crystallization. 

(6)  The  effects  of  heating. 


9      .     10     .     1,1  12     .     1,3     .     1,4  1,5     ,     1,6 


4^iiiililyiii"iiiiiiiiii'iiiiiiiiiiiliiiii^ 


1.0     .     1.1     .     1,2  13  1.4     .     1.5     .     1,6 


7      .      8      .      9      .     1.0     .     1,1     .     12     ,     1,3    ,     1.4     ,     1,5 


timkl 


10     .     1,1     .     1,2     .     1,3     ,    14     ,     1,5     ,      1,6 


lllllllllllllllllllllllllllllllllilllllllllllllllll! 


1.0     .     1.1     .     1.2     .     1.3     .     1,4     .     1.5     .     16 


'4mllTlllll"llllllllllll"llllH!lillllllllllllllHlllllllll!llH^ 


2.3.4 


1,0     .     1,1     .     12     .     13  1.4     .      15     .      1.6 


Fig.  1. — 1.  Uranic  nitrate.  2.  Uranic  acetate.  3.  Sodio-uranic  acetate.  4.  Uranic  oxychlo- 
ride  (acid),  mixed  hydrates.  5.  Potassio-uranic  oxychloride.  6.  Uranic  oxyfluoride.  7.  Bario- 
uranic  oxyfluoride.  8.  Uranic  phosphate,  mixed  hydrates.  9.  Calcio-uranic  phosphate. 
10.  Ammonio-uranic  sulphate. 


HISTORICAL.  9 

Morton  and  Bolton,  like  Becquerel,  refer  to  the  possibility  of  deter- 
mining the  composition  of  uranyl  compounds  from  the  observation  of 
their  fluorescence  spectra  and  state  that  even  minute  quantities, 
present  as  impurities,  may  be  detected  by  means  of  their  characteristic 
bands. 

Hagenbach^  likewise  published  a  considerable  list  of  fluorescence 
bands  for  the  uranyl  salts,  but  his  paper  adds  little  to  the  data  of 
Becquerel  and  of.  Morton  and  Bolton. 

In  1903,  J.  Becquerel  and  Onnes,  working  in  the  cryogenic  laboratory 
at  Leyden,  excited  various  uranyl  salts  to  fluorescence  at  the  tempera- 
tures of  liquid  air  and  of  liquid  hydrogen  respectively. 

At  —185°  C.  each  band  of  the  spectrum  was  found  to  be  resolved 
into  a  group  of  much  narrower  bands.  The  spectra  of  a  number  of 
compounds  were  photographed,  using  a  grating  spectrograph,  and  the 
most  prominent  bands  were  mapped. 

It  was  shown  in  the  course  of  this  investigation  that  the  resolved 
spectra  are  made  up  of  series  of  bands,  the  frequency  interval  varying 
slightly  for  different  compounds;  also  that  each  group  in  a  given  spec- 
trum is  similar  to  all  the  other  groups  as  regards  the  arrangement  and 
the  relative  intensities  of  its  components.  In  the  reversing  region, 
where  fluorescence  goes  over  into  absorption,  the  coincidence  in  posi- 
tion of  bright  and  dark  bands  was  pointed  out.  Further  cooling  to 
the  temperature  of  liquid  hydrogen  rendered  the  individual  bands 
sharper  and  more  line-like,  but  there  was  no  further  resolution. 

This  resolution  of  the  fluorescence  spectra  by  cooling  constitutes  the 
most  important  advance  subsequent  to  the  discoveries  of  Stokes  and 
of  E.  Becquerel,  since  it  affords  a  means  of  studying  the  more  intimate 
structure  of  these  remarkable  spectra.  It  forms,  indeed,  the  starting- 
point  for  the  present  investigation. 

1  Hagenbach,  Annalen  der  Physik.,  v.  146,  p.  395.     1872. 


II.  THE  STRUCTURE  OF  FLUORESCENCE  SPECTRA. 


A  fluorescence  spectrum  consists  of  one  or  more  bright  bands,  and 
these  may  greatly  vary  in  width,  from  the  very  broad  bands,  fiUing  a 
great  part  of  the  visible  spectrum,  characteristic  of  the  fluorescent 
dyestuffs  and  the  phosphorescent  sulphides,  to  the  line-like  bands  of 
the  ruby. 

Such  a  spectrum  is  either  a  homogeneous  complex  of  systematically 
related  components  or  a  heterogeneous  complex  of  unrelated  compo- 
nents. In  either  case  the  components  frequently  overlap,  giving  the 
appearance  of  a  single  band,  which  may  be  described  as  a  mixed  hand 
(an  unresolved  heterogeneous  complex)  or  a  homogeneous  band,  respec- 
tively. Where  the  components  overlap  less  completely  or  not  at  all  the 
appearance  is  that  of  a  group  of  bands. 

It  is  probable  that  a  heterogeneous  complex  is  always  the  result  of 
a  mixture  of  two  or  more  compounds  the  fluorescence  of  each  of  which 
by  itself  gives  a  homogeneous 
complex. 

The  phosphorescent  sul- 
phides afford  spectra  which 
may  serve  to  illustrate  the 
above  classification.  A  stron- 
tium sulphide  with  bismuth  as 
the  active  metal  and  a  flux  of 
sodium  sulphate,  for  example, 
has  a  fluorescence  spectrum 
which  appears  to  the  eye  to 
consist  of  a  single  band  with 
its  crest  at  0.480  /jl,  A  recent 
spectrophotometric  explora- 
tion by  Dr.  H.  L.  Howes,^ 
however,  shows  a  group  of 
closely  over-lapping  compo- 
nents (see  fig.  2).  The  crests 
of  these  are  located  as  shown 
in  table  1;  and  as  they  are 
systematically  related,  form- 
ing members  of  a  series  having 
a  uniform  interval  of  frequency 
difference,  this  is  to  be  regarded 
as  a  homogeneous  band  or  homogeneous  complex. 

Similarly,  the  fluorescence  of  a  barium  sulphide  with  copper  as  the 
active  metal  and  a  flux  of  sodium  borate,  when  viewed  through  an 


Fig.  2. 


Proceedings  American  Philosophical  Society,  lvi,  p.  258.     1917. 


10 


GENERAL   DISCUSSION   OF   FLUORESCENCE   SPECTRA. 


11 


ordinary  spectroscope,  has  a  spectrum  which  seems  to  consist  of  a 
single  very  broad  band.  A  spectrophotometric  study  reveals,  how- 
ever, two  neighboring  and  overlapping  bands.  These  have  their  crests 
in  the  red  and  green  respectively  and  are  complex.     (See  fig.  3.) 

Table  1. — Approximate  wave-lengths  of  visible  crests  in  the  spectrum  of  a  phosphorescent 
strontium  sulphide  (Sr;  Bi;  Na2S0),  No.  IS. 


M- 

Visible 

crests 

1/mX103. 

Intervals. 

M- 

Visible 

crests 

1/mX103. 

Intervals. 

0.4430 
.4547 
.4670 
.4801 
.4938 

2257 
2199 
2141 
2083 
2025 

58 
58 
58 
58 

0.5238 

1909 

2X58 

.5562 

1793 

2X58 

.5921 

1677 

2X58 

The  components  of  the  band  in  the  green  are  members  of  a  series 
having  a  constant  frequency  interval  of  70  (see  table  2),  while  the 
components  of  the  band  in  the  red  form  a  series  with  an  interval  of 


Fig.  3. 

26.6.  The  two  series  overlap,  as  may  be  seen  from  figure  3.  In  this 
example  the  spectrum  as  a  whole  forms  a  heterogeneous  complex  made 
up  of  two  homogeneous  complex  bands  which  are  partially  super- 
imposed. 

The  fluorescence  spectrum  of  commercial  anthracene  affords  an 
example  of  a  heterogeneous  complex  easily  resolved  into  a  group  of 


12 


FLUORESCENCE   OF   THE   URANYL   SALTS. 


bands.  There  are  at  least  7  such  bands,  4  of  which  are  seen  in  the 
spectroscope  with  a  region  in  the  violet  not  readily  resolved  by  visual 
observations.  This  violet  fluorescence  has,  however,  been  determined 
photographically  by  Miss  McDowell.^  The  approximate  location  of 
the  bands  in  this  spectrum  is  shown  in  figure  4. 

Table  2. — Approximate  wave-lengths  and  frequencies  of  visible  crests  in  the  spectrum  of  a 
phosphorescent  barium  sulphide  (Ba;  Cu;  Na2B407). 


Green  complex. 

Red  complex. 

Visible 
crests. 

Intervals. 
1/mX103. 

Visible 
crests. 

Intervals. 
l/fiXlOK 

0.4255 
.4386 

70 

0.5000 

26.6X2 

70X2 

70 

70 

.5136 

.4673 
.4831 
.5000 

26.6X2 

.5283 

26.6X7 

70X2 

.5861 

.5376 

26.6X2 
"26!6><2"' 

.6049 

.6250 

26.6X2 
26.6 

.6465 
.6578 
.6695 

26.6 

While  all  of  these  bands  are  pressnt  in  the  fluorescence  of  the  impure 
commercial  product,  they  are  not  all  due  to  any  one  constituent.  By 
solution  and  subsequent  fractional  sublimation,  as  is  well  known,  it 
is  possible  to  partially  separate  the  substance  into  pure  anthracene, 
which  has  a  violet  fluorescence  and  a  residue  containing  chrysogen,  the 
fluorescence  of  which  is  green. 


Fig.  4. 


Miss  McDowell  has  shown  that  the  bands  6,  7,  and  8  belong  to  the 
anthracene  thus  obtained,  while  band  4  is  also  present  in  its  spectrum. 
Bands  1,  2,  3,  and  4  are  characteristic  of  the  green  residue. 

1  Miss  L.  S.  McDowell,  Physical  Review  (1),  xxvi,  p.  155.     1908. 


GENERAL   DISCUSSION   OF   FLUORESCENCE    SPECTRA. 


13 


The  presence  of  band  4  in  both  spectra  may  be  due  to  the  imperfect 
separation  of  the  two  substances.  That  it  is  much  stronger  in  spectra 
obtained  from  mixtures  showing  green  fluorescence  than  from  those 
the  fluorescence  of  which  is  blue-violet  would  seem  to  warrant  ascribing 
it  to  the  chrysogen  component,  a  conclusion  strengthened  by  the  con- 
sideration of  the  placing  of  the  bands.  The  most  probable  positions 
of  the  crests  are  given  in  table  3.  The  positions  of  the  three  bands 
assigned  to  anthracene  are  from  photographic  measurements  by  Miss 
McDowell;^  those  due  to  chrysogen  are  from  spectrophotometric  read- 
ings made  in  1910,^  combined  with  more  recent  observations. 

Table  3. — Wave-lengths  and  frequencies  of  the  hands  of  commercial  anthracene. 


Band. 

At- 

1/mX10'. 

Difference. 

1. 
2. 
3. 
4. 
6. 
6. 
7. 

0.6235 
.5790 
.5362 
.5005 
.4750 
.4490 
.4260 

1603 
1733 
1860 
1996 
2105 
2227 
2347 

130 
127 
136 

Chrysogen . . . 

122 
120 

Anthracene. . . 

It  will  be  noted  that  the  three  bands  in  the  blue-violet  are  members 
of  a  series  having  a  frequency  interval  of  about  121;  also  that  the 
4  bands  of  greater  wave-length  form  a  series  with  a  somewhat  greater 
interval,  ^.  e.,  about  131.  Band  4  is  too  near  to  band  5  to  belong 
to  the  anthracence  series,  but  may,  within  the  rather  large  errors 
due  to  the  breadth  and  vagueness  of  these  bands,  be  regarded  as  one 
of  the  chrysogen  series. 

There  are  several  criteria  based  on  experimentally  established  facts 
by  which  the  homogeneity  or  heterogeneity  of  a  fluorescence  band  or 
complex  may  be  determined. 

CRITERIA  OF    HOMOGENEITY. 

(1)  The  position  and  distribution  of  intensities  in  a  homogeneous 
band  is  independent  of  the  mode  of  excitation.  This  was  established 
by  various  observations  published  several  years  ago,^  and  subsequent 
experience  strengthens  our  conviction  that  it  is  a  general  principle  and 
that  shifts  in  position  and  change  of  form  are  to  be  regarded  as  indica- 
tions of  heterogeneity  due  to  the  presence  of  more  than  one  lumines- 
cent substance. 

(2)  The  distribution  of  intensities  in  a  homogeneous  band  is  such 
that  the  curve  has  a  single  well-marked  maximum.  The  slope  toward 
the  violet  is  steeper  than  that  toward  the  red,  like  that  in  the  corre- 
sponding curve  of  intensities  of  an  incandescent  black  body. 

1  Miss  L.  S.  McDowell,  1.  c. 

'  Nichols,  E.  L.,  Proc.  Am.  Philos.  Soc,  xlix,  p.  277. 

'  See  Nichols  and  Merritt,  Studies  in  Luminescence,  Carnegie  [Inst.  Wash.  Pub.  No.  152,  pp. 
24,  38,  144. 


14 


FLUORESCENCE    OF   THE    URANYL   SALTS. 


In  the  case  of  a  partially  resolved  or  wholly  resolved  homogeneous 
complex  the  envelope  obtained  by  drawing  a  curve  through  the  crests 
of  the  group  of  bands  has  the  above  form,  as  has  the  curve  of  intensities 
of  each  of  the  component  bands. 

A  departure  from  this  type  indicates  heterogeneity.  Thus,  for 
example,  the  curve  in  figure  2  suggests  a  partially  resolved  homogeneous 
complex,  while  that  in  figure  3  indicates  a  heterogeneous  complex  or 
mixed  band. 

The  best  examples  thus  far  are  found  among  the  uranyl  salts.   Figure  5 
shows  a  typical  case  in  which  the  envelope  of  the  7  bands  of  a  uranyl 
salt  is  shown  and  with  an  enlarged  scale  of  wave-lengths  the  distribu- 
tion of  intensities  of  a  single 
band   of  the  same  spectrum. 
Other    illustrations     will     be 
found  in  subsequent  chapters 
of  this  monograph. 

(3)  In  a  homogeneous  com- 
plex, the  fluorescence  spectrum 
is  identical  with  that  observed 
during  phosphorescence  as 
regards  the  position,  relative 
intensity,  and  structure  of 
its  component  bands.  Nor  is- 
there  any  change  in  these 
respects  during  the  process  of 

decay.  Change  of  color  in  passing  from  the  fluorescent  to  the  phos- 
phorescent stage  or  during  phosphorescence  is  therefore  a  criterion  of 
heterogeneity,  since  such  changes  are  due  to  the  presence  of  bands 
having  different  rates  of  decay. 

Such  subjective  changes  of  color  as  are  due  to  the  loss  of  intensity 
during  decay  are  excluded  from  the  above  statement. 

Most  of  the  phosphorescent  sulphides  afford  examples  of  heterogene- 
ity clearly  indicated  by  the  above  criterion  and  confirmed  in  other  ways, 
while  the  spectra  of  the  uranyl  salts,  in  spite  of  their  great  complexity, 
are  found,  from  this  criterion,  too,  strictly  homogeneous. 

(4)  Persistence  of  color  and  of  structure  when  excited  to  fluorescence 
at  different  temperatures,  the  different  components  of  the  spectrum 
suffering  the  same  relative  changes  of  intensity,  may  be  regarded  as  a 
criterion  of  homogeneity,  but  the  complex  changes  of  structure  revealed 
by  the  resolution  of  spectra  in  the  process  of  cooling  to  the  temperature 
of  liquid  air  do  not  necessarily  indicate  heterogeneity. 

As  will  be  shown  in  subsequent  chapters,  the  fluorescent  spectra  of 
the  uranyl  salts,  for  example,  are  profoundly  modified  by  the  cooling 
of  the  substance,  and  yet  these  spectra  conform  to  all  other  known 
criteria  of  homogeneity. 


Fig.  5. 


III.  PRELIMINARY  OBSERVATIONS  ON  CERTAIN 
URANYL  SALTS.i 

Because  of  their  brilliant  luminescence  and  the  interesting  character 
of  their  spectra  of  fluorescence  and  absorption,  the  uranyl  compounds 
have  been  the  subject  of  extended  study.  A  brief  account  of  the  work 
of  previous  observers  in  this  field  has  been  given  in  Chapter  I. 

Our  original  purpose  in  taking  up  the  study  of  these  substances  was 
to  determine  whether  the  different  bands  of  the  fluorescence  spectrum 
are  to  be  regarded  as  independent,  each  with  its  own  region  of  excita- 
tion, or  whether  they  form  a  homogeneous  complex,  such  that  the 
excitation  of  one  necessarily  involves  the  excitation  of  all.  In  this 
inquiry  we  have  been  led  to  the  investigation  of  many  other  questions. 

Since,  as  was  first  shown  by 


C>0O 


L.B. 


Becquerel  and  Onnes^  in  the  paper 
cited  in  Chapter  I,  the  bands  of 
the  uranyl  salts  are  resolved  into 
groups  of  narrow  components  by 
cooling,  it  is  at  the  temperature 
of  liquid  air  and  chiefly  by 
photographic  methods  that  the 
intimate  structure  of  the  fluo- 
rescence and  absorption  spectra 
is  to  be  determined.  The  study 
of  the  spectra  at  ordinary  tem- 
peratures, however,  is  not  without 
significance. 

In  this  work,  where  the  width 
of  the  bands  is  from  50  to  100 
A.  TJ.,  the  spectrophotometer  is 
indispensable.  Many  of  the 
measurements  to  be  described 
were  made  with  a  special  in- 
strument which   combines    the 

features  of  the  constant  deviation  spectrometer  and  the  Lunamer- 
Brodhun  spectrophotometer.  It  is  essentially  a  spectrometer  of  the 
Hilger  type,  with  two  collimators  C  and  C  (fig.  6),  a  Lummer-Brodhun 
cube  L.  B.,  and  a  constant-deviation  prism  P  with  carefully  calibrated 
drum. 

1  Certain  of  the  observations  contained  in  this  chapter  have  been  published  in  the  Physical 
Review  (1),  xxxiii,  p.  355,  but  many  of  the  data  there  given  have  been  replaced  by  more  complete 
investigations  kindly  done  at  our  request  by  Dr.  Frances  G.Wick  (Physical  Review  (2) ,  v.  11,  p.  121. 
Feb.  1918. 

'  Becquerel  and  Onnes,  Leiden  Communications,  110.     1909. 

15 


Fig.  6. 


16 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


For  the  determination  of  wave-lengths  the  eyepiece  is  provided  with 
a  pointer  in  the  focal  plane  and  also  with  the  usual  slides  for  isolating 
the  region  under  observation. 

The  collimator  slits  have  micrometric  adjustment,  and  to  provide 
for  convenient  comparison  through  the  very  great  range  of  intensities 
occurring  in  the  study  of  fluorescence,  the  illumination  of  the  com- 
parison slit  can  be  varied  by  moving  the  comparison  light  along  a 
photometer  bar  to  any  desired  distance  from  the  slit.  The  observing 
telescope  can  be  replaced  by  a  camera  whenever  photographs  of  the 
spectra  are  desired.  With  this  instrument  the  wave-lengths  of  the 
bands  could  be  determined  by  setting  the  pointer  to  the  region  of 
greatest  brightness  as  estimated  by  the  eye  and  the  relative  intensities 
could  be  measured  spectrophometrically. 

Tables  4  to  10  contain  the  resulting  data  for  several  salts;  also  the 
frequencies  corresponding  to  the  wave-lengths  and  frequency  intervals. 
The  measurements  and  computations  were  kindly  made  by  Miss  Wick, 
who  likewise  determined  the  relative  brightness  of  the  bands  in  several 
of  the  spectra. 

From  the  data  in  these  tables  some  of  the  salient  features  of  the 
uranyl  spectra  may  be  deduced,  viz: 

(1)  The  weakest  bands  are  at  the  ends  of  the  spectrum,  i.e.,  in  the 
red  and  the  blue. 

(2)  The  brightest  band  is  not  in  the  center,  being  third  from  the 
violet  end  and  sixth  from  the  red  end  when  all  8  bands  of  the  spectrum 
are  visible. 

(3)  Taking  the  frequency  intervals,  instead  of  the  differences  of 
wave-length,  the  bands,  with  the  exception  of  the  band  of  shortest 
wave-length  (band  8),  are  equidistant,  at  least  within  the  rather  large 

Table  4. — Fluorescence  hands  of  the  nitrates. 


Uranyl  nitrate  (Anhydrous);  (UO2 
(N03)2).      Width   of   bands  about 
70  A.  u. 

Uranyl    nitrate    (tri-hydrate)    (UO2 
(N03)2+3H20).    Observations  on  a 
single  large  crystal ;  width  of  bands 
about  100  A.  U. 

Uranyl  nitrate  (hexahy- 
drate)      (U02(N03)2+6 
H2O). 

Position 
of  crest 
of  band. 

I/mXIO'. 

Inter- 
val. 

Inten- 
sity. 

Position 
of  crest 
of  band. 

1/mX103. 

Inter- 
val. 

Inten- 
sity. 

Position 
of  crest 
of  band. 

1//XX103. 

Inter- 
val. 

4720.0 

2118.6 

65.8 

4871.0 

2052.9 

84.3 

49.2 

4720.8 

2118.2 

69.8 

4871.2 

2052.8 

88.2 

50.2 

5079.7 

1968.6 

86.8 

100.0 

4881.8 

2048.4 

86.4 

6090.0 

1964.6 

87.6 

100.0 

6314.0 

1881.8 

87.6 

64.6 

5096.3 

1962.0 

86.1 

6327.6 

1877.0 

87.4 

52.7 

5573.4 

1794.2 

87.4 

20.0 

5330.6 

1875.9 

87.3 

6687.6 

1789.6 

87.2 

25.1 

5859.0 

1706.8 

84.6 

5591.2 

1788.6 

87.2 

6874.0 

1702.4 

84.7 

6164.3 

1622.2 

5877.5 

1701.4 

86.0 

6181.2 

1617.7 

6186.5 

1616.4 

FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.       17 
Table  5. — Fluorescence  bands  of  the  double  nitrates. 


Ammonium   uranyl    nitrate    08),  U02(N03)2-NH4 
NOs.  (Accuracy  of  setting  not  to  be  expected; 
the  double  crest  (a  and  6)  of  each  band  is  flat 
of  nearly  equal  intensity,  rather  broad,  and  not 
well  separated.) 

Potassium  uranyl  nitrate, 
U02(N03)2KN03. 
(Bands  broad    and   fuzzy;    over  100  units  wide; 
crests    distinctly    double,    with    a   third    crest 
toward  the  violet.) 

Position  of 

crest  of 

band. 

i/m+103. 

Interval, 

Position  of 

crest  of 

band. 

1/mX103. 

Jnterval. 

a-a 

6-6 

a-a. 

6-6. 

a-4639.6 
6-4705.3 

a-4800.0 
6-4841.6 

a-4992.6 
6-5048.3 

a-5224.0 
6-5280.6 

a-5473.0 
6-5535.6 

a-5748.7 
6-5825.6 

a-6026.6 
6-6130.8 

2155.3 
2125.0 

2083.3 
2065.4 

2003.0 
1980.8 

1914.2 
1893.6 

1827.1 
1806.5 

1739.5 
1716.5 

1659.3 
1631.0 

a-4696.0 

a-4860.0 
6-4904.0 

a-5077.5 
6-5108.3 

a-5303.5 
6-5347.0 

a-5556.0 
6-5607.3 

a-5836.5 
6-5891.5 

a-6146.3 
6-6209.0 

2129.5 

2057.6 
2039.0 

1969.4 
1957.5 

1885.5 
1870.2 

1799.8 
1783.5 

1713.3 
1697.3 

1627.0 
1610.6 

71.9 

72.0 

59.6 

88.2 

81.6 

80.3 

84.6 

83.7 

87.3 

88.8 

87.2 

85.7 

86.7 

87.1 

87.1 

86.6 

86.2 

87.6 

90.0 

86.3 

86.7 

80.2 

85.5 

Table  5. — continued. 


Rubidium  uranyl  nitrate, 
U02(N03)2-RbN03. 
(Bands  very  broad  with  two  poorly  defined  crests. 
With    less  "excitation  the  bands  appear  single. 
Settings  are  only  roughly  approximate.) 

Position  of 
crest  of 
band. 

1//XX103. 

Internal. 

Intensity. 

a-a. 

6-6. 

6-6. 

6-4828.0 

a-4994.5 
6-6045.5 

ar^210.7 
6-5265.3 

cj-5454.6 
6-6625.0 

a-6738.8 
6-6820.5 

O-6012.0 
6-6119.0 

2071.0 

2002.2 
1982.0 

1919.2 
1899.0 

1833.3 
1810.0 

1742.6 
1718.0 

1663.0 
1634.0 

89.0 

68.3 

83.0 

83.0 

100.0 

85.9 

89.0 

39.4 

90.7 

92.0 

7.6 

79.6 

84.0 

2.1 

Table  6. — Fluorescence  bands  of  the  sulphate. 

Uranyl  sulphate  (UO2SO4+3H2O). 

Position  of 

crest  of 

band. 

l/juXl0». 

Interval. 

Intensity. 

a-a. 

6-6. 

a. 

6. 

a— 

6-0.4753 

a-  .4886 
6-  .4941 

a-  .5099 
6-  .5158 

a-  .5335 
6-  .5397 

a-  .5592 
6-  .5662 

a-  .5877 
6-  .5962 

a-  .6183 
6-  .6284 

2103.9 

2041.7 
2023.9 

1961.0 
1938.7 

1874.4 
1852.9 

1788.3 
1766.2 

1701.6 
1677.3 

1617.3 
1590.2 

80.0 

85.7 

86.2 

27.97 

38.72 

86.6 

86.8 

91.79 

100.00 

86.1 

86.7 

60.04 

63.79 

86.8 

88.9 

19.27 

20.14 

84.2 

87.1 

18 


FLUORESCENCE    OF   THE    URANYL   SALTS. 


uncertainties  inevitable  in  the  attempt  to  locate  the  crests  of  such 
broad  bands.  Of  this  band,  which  occupies  the  region  lying,  roughly, 
between  0.4650  fx  and  0.4750  /x,  only  the  less-refrangible  edge  is  seen, 
the  other  side  being  more  or  less  cut  off  by  absorption.  Its  apparent 
distance  from  band  7  is  thus  reduced. 

(4)  In  some  cases  there  is  sufficient  evidence  of  resolution  to  enable 
the  location  of  two  or  more  crests.  Further  evidences  of  complexity 
will  be  found  in  the  spectrophotometric  study  of  these  spectra,  to  be 
considered  in  a  subsequent  paragraph. 

Table  7. — Fluorescence  bands  of  the  double  sulphates. 


Sodium  uranyl  sulphate  (UO2SO4 .  Na2S04) . 

Potassium  uranyl  sulphate  (UO2SO4.K2SO4). 

Position  0  f 
crest  of 
band. 

1/fxXlOK 

Interval. 

Intensity. 

Position  of 

crest  of 

band. 

1/MX103. 

Interval. 

Intensity. 

4744.0 
4910.0 
5125.0 
5354.2 
5608.4 
5890.5 
6200.2 

2107.9 
2036.6 
1951.0 
1867.6 
1783.0 
1697.6 
1612.8 

71.3 
85.6 
83.4 
84.6 
85.4 
84.8 

4778.0 
4935.5 
5133.6 
5365.6 
5619.2 
5902.9 
6201.2 

2093.0 
2026.1 
1948.0 
1863.7 
1779.5 
1694.3 
1612.6 

66.9 
78.1 
84.3 
84.2 
85.2 
81.7 

27.29 

100.00 

46.77 

15.13 

5.88 

35.33 

100.00 

41.22 

12.85 

Ammonium  uranyl  sulphate  (UO2SO4.  (NH4)2S04). 
(The  two  crests  of  each  band  very  close  and  narrow.) 

Rubidium  uranyl  sulphate 
(UOzSOi-RbzSO*). 

Position  of 

crest  of 

band. 

1//XX103. 

Interval. 

Intensity. 

Position  of 

crest  of 

band. 

I/mXIO'. 

Interval. 

Intensity. 

a-a. 

6-6. 

a-4929.0 
6-4950.0 

a-5140.8 
6-5164.8 

a-5374.5 
6-5399.5 

a-5627.0 
6-5657.8 

a-5906.5 
6-5935.5 

a-6213.7 
6-6251.4 

2028.8 
2020.2 

1945.2 
1936.2 

1860.6 
1852.0 

1777.0 
1767.5 

1693.0 
1684.8 

1609.3 
1599.6 

83.6 

84.6 
83.6 
84.0 

83.7 

84.0 

84.2 
84.5 
82.7 
85.2 

25.5 

4757.0 

4930.0 

5136.0     • 

5368.7 

5619.8 

5894.0 

6195.5 

2102.2 
2028.3 
1947.4 
1862.6 
1779.4 
1696.6 
1614.1 

73.9 
80.9 
84.8 
83.2 
82.8 
82.5 

38.52 

100.00 

49.35 

19.77 

100.00 

21.43 

11.86 

m  iskm  tk 

1 

FLUORESCENCE  AND  ABSORP 

Table  7. — Fluorescence  hands  of  the  dovble  sulphates — 

continued. 

Uranyl  cjBsium  sulphate  (UO2SO4 .  CSSO4) . 

(Bands  over  100  units  wide  with  sharp  maxima  near 

the  end  toward  red  and  secondary  maxima  (brack- 

eted) much  less  bright  and  sharp  toward  the  violet.) 

Wave-length 

of  crest  of 

1/aiX103. 

Interval. 

Intensity. 

hand. 

4702.0 

2126.7 

75.8 

4876.0 

2050.9 

50.49 

(4933.0) 

85.7 

5088.5 

1965.2 

100.00 

(5151.5) 

84.4 

5317.0 

1880.8 

53.09 

(5338.0) 

86.6 

5573.5 

1794.2 

16.90 

(5670.0) 

85.4 

5852.0 

1708.8 

86.8 

6.36 

6165.0 

1622.0 

3N  OF  THE  URANYL  SALTS.       19 
Table  8. — Fluorescence  bands  of  two  acetates. 


RELATIVE  INTENSITIES    OF   THE 
BANDS. 

To  indicate  graphically  the 
relative  intensities  of  the  bands, 
we  may  plot  their  strength,  ex- 
pressed in  terms  of  energy,  as 
ordinates  and  wave-lengths  of  the 
crests  as  abscissae. 

The  resulting  curve  (see  figs. 
7,  8,  9,  and  10)  is  a  sort  of  enve- 
lope for  the  entire  spectrum  cor- 
responding to  the  curve  of  distri- 
bution of  energy.  It  resembles  in 
type  the  curve  of  energy  found 
in  the  case  of  the  broad,  single- 
banded  fluorescence  described  in 
earlier    communications,^    being 

single-crested  and  steeper  toward  the  violet.  As  has  been  pointed 
out  in  Chapter  II,  these  curves  are  very  similar  to  the  energy  curve 
for  temperature  radiation. 

Figure  7  contains  the  envelopes  thus  plotted  of  5  uranyl  double 
sulphates.  Of  these,  4  have  their  crests  at  approximately  the  same 
wave-length  (0.515 /x).  Curve  E  (caesium  uranyl  sulphate)  is  shifted 
slightly,  an  effect  due  to  the  presence  of  a  strong  component  of  each 
band  on  the  violet  side  of  the  main  crest  which  influences  the  estimates 

^  Nichols  and  Merritt,  Physical  Review  (1),  xviii,  p.  403;  xix,  p.  18. 


Uranyl  acetate. 

Position  of 

crest  of 

band. 

1/fxXlOK 

Interval. 

Intensity. 

4710.0 
4878.0 
5094.0 
5328.0 
5586.0 
5869.2 
6182.3 

2123.0 
2050.0 
1963.1 
1876.9 
1790.2 
1703.8 
1617.5 

73.0 
86.9 
86.2 
86.7 
86.4 
86.3 

48.16 
100.00 
48.86  . 
22.36 

Ammonium  uranyl  acetate. 

Position  of 
crest  of 
band. 

1/mX10'. 

Interval. 

Intensity. 

a-a. 

6-6. 

6-4680.0 

a-^804.5 
6-4884.3 

a-5016.3 
6-5094.6 

0-5242.2 
6-5330.8 

a-5487.8 
6-5581.0 

a- 

6-5870.6 

a- 

6-6207.5 

2136.0 

2081.3 
2047.4 

1993.5 
1962.9 

1907.5 
1875.9 

1822.2 
1791.7 

87.8 
86.0 
85.3 

88.6 
84.5 
87.0 

84.2 
88.3 
92.5 

61.42 

100.00 

46.12 

18.40 

1703.4 

1610.9 

20 


FLUORESCENCE    OF  THE   URANYL   SALTS. 

Table  9. — Fluorescence  hands  of  two  phosphates. 


Uranyl  phosphate  (H-U02-P04). 
(Bands  narrow  and  distinct.) 

Ammonium  uranyl  phosphate 

(H,(NH4)2U02(P04)2).  (Bands  very 

distinct  with  narrow  crests.) 

Position  of 

Position  of 

crest  of 

I/mXIO'. 

Interval. 

crest  of 

1/mX103. 

Interval. 

band. 

band. 

4847.0 

2063.0 

71.7 

4845.0 

2063.9 

69.7 

5020.3 

1991.9 

83.8 

5014.6 

1994.2 

82.7 

5240.7 

1908.1 

83.7 

5231.3 

1911.5 

83.2 

6481.1 

1824.4 

■ 

84.9 

5469.6 

1828.3 

83.7 

5748.6 

1739.5 

82.9 

5730.8 

1744.6 

83.8 

6036.5 

1656.6 

6021.0 
6336.0 

1660.8 
1578.3 

82.5 

Table  10. — Flitorescence  hands  of  a  nitrate,  oxalate,  and  fluoride. 


Uranyl  nitrate 

Uranyl  oxalate 

Potassium  uranyl  fluoride 

(U02(N03)2-6H20). 

U02C204-3H20. 

(UO2  F2-2KF). 

Position  of 

Position  of 

Position  of 

crest  of 

1/mX103. 

Interval. 

crest  of 

l/lxXlO\ 

Interval. 

crest  of 

1/aiX103. 

Interval. 

band. 

band. 

band. 

4700.0 

2127.6 

72.1 

4715.0 

2120.9 

75.1 

4865.0 

2055.5 

89.3 

4888.0 

2045.8 

92.3 

4803.2 

2081.9 

79.8 

5085.8 

1966.2 

86.6 

5119.0 

1953.5 

86.3 

4994.8 

2002.1 

86.8 

5320.0 

1879.6 

88.3 

5355.0 

1867.2 

86.9 

5219.5 

1915.3 

85.6 

5582.3 

1791.3 

87.0 

5617.0 

1780.3 

88.2 

5465.2 

1829.7 

89.1 

5867.0 

1704.3 

86.2 

5910.0 

1692.1 

88.2 

5745.0 

1740.6 

89.1 

6179.8 

1618.1 

6235.0 

1603.9 

6055.0 

1651.5 

of  the  location  of  the  latter.  The  envelopes  of  the  4  nitrates  in  figure  8 
have  the  same  characteristics.  The  crests  of  3  agree  (at  0.510 /z), 
while  the  envelope  D  of  rubidium  uranyl  nitrate,  in  the  spectrum  of 
which  the  bands  are  vaguely  double-crested,  is  displaced.  In  the  two 
uranyl  acetates  (fig.  9)  the  same  identity  of  type  and  position  shows 
itself. 

To  reduce  these  spectrophotometric  measurements  to  relative  energy 
units  the  distribution  curve  of  the  comparison  light  must  be  known. 
This  curve  for  the  acetylene  flame,  which  was  the  source  employed, 
has  been  carefully  determined,  and  data  published  by  Coblentz  were 
used  in  the  computation. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      21 


In  certain  cases  the  resolution  of  the  bands  is  such  that  the  brightness 
of  two  crests  can  be  determined  and  two  overlapping  envelopes  drawn, 
as  in  figure  10,  which  pertains  to  the  spectrum  of  UO2SO4+3H2O.  The 
relative  brightness  of  the  two  crests  is  seen  to  vary  slightly  from  band 
to  band. 


Fig.   7. 


Fig.  8. 


The  changes  in  the  position  of  the  crests  in  the  case  of  the  sulphates, 
nitrates,  and  acetates  is  illustrated  in  figure  11,  in  which  a  typical  curve 
from  each  family  of  salts  is  given. 

While  these  measurements  by  Dr.  Wick  do  not  include  all  the  spectra 
for  which  such  determinations  are  possible,  they  suffice  to  demonstrate 
the  essential  uniformity  of  type  of  the  envelopes  and  to  show  that 
within  a  given  family,  such  as  the  double  sulphates  or  the  nitrates,  the 
crests  occupy  the  same  region  in  the  spectrum.  It  will  be  seen,  when 
we  come  to  the  consideration  of  the  detailed  structure  of  these  fluores- 
cence spectra,  that  there  is  a  slight  but  definite  shift  of  all  the  bands 
with  molecular  weight. 

Spectrophotometric  measurements  of  single  unresolved  bands,  prac- 
ticable with  accuracy  only  in  the  case  of  some  of  the  brightest,  show  the 


22 


FLUORESCENCE   OF   THE   URANYL   SALTS. 


curve  of  distribution  to  be  of  the  same  type  as  that  obtained  when  the 
envelope  is  drawn  for  the  entire  spectrum,  i.  e,,  the  type  associated 
with  what  we  have  termed  a  simple  band.  (See  A  in  fig.  5,  Chapter  II, 
which  is  the  energy  curve  for  the  brightest  band  of  uranyl  potassium  sul- 


FiG.  9. 


Fig.  10. 


phate  with  the  scale  of  wave-lengths,  adjusted  so  as  to  make  the  width 
nearly  the  same  as  that  of  the  envelope  (B)  for  the  same  substance.) 

The  most  striking  feature 
distinguishing  these  spectra 
from  one  another  to  the  eye, 
excepting  where  partial  resolu- 
tion occurs,  is  the  varying  width 
and  sharpness  of  the  bands. 

With  the  spectrophotometer 
it  is  possible  to  obtain  a  more 
definite  expression  of  this  fea- 
ture, as  may  be  seen  from  fig- 
ures 12  and  13,  in  which  are 
depicted,  from  such  measure- 
ments, the  three  brightest  bands 
of  uranyl  nitrate  (crystallized) 
and  uranyl  potassium  sulphate. 
It  will  be  noted  that  the  bands 
overlap  at  the  base,  but  to  a 
greater  extent  in  the  nitrate 
than  in  the  potassium  sulphate,  where  the  bands  are  narrower  and 
more  sharply  defined. 


-    1 

I      .55/i, 

/ 

.50^ 

^ 

V 

\ 

^m 

IftlOO 

20100 

Fig.  11. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      23 


A  more  detailed  use  of  the  instrument,  working  with  narrow  slits  and 
making  settings  at  closer  intervals,  will  often  bring  out  the  complexity 
of  single  bands,  where  the  overlapping  of  the  components  is  such  as  to 
conceal  the  structure  Figures  14,  15,  16,  and  17  give  the  results  of 
such  a  study  by  Miss  Wick.     The  existence  of  numerous  partly  sub- 


t 

8 

fl 

A 

\ 

• 

^ 

• 

i 

\ 

T 

\ 

\          A 

■ 

A 

' 

\J 

\  A 

2 

\ 

\ 

A 

T 

.52^ 

} 

V 

^ 

h 

Fig.  12.  Fig.  13. 

Showing  the  relative  intensities  of  the  brightest  fluorescence  bands  of  uranyl 

nitrate  (fig.  13)  and  uranyl  potassium  sulphate  (fig.  14). 

merged  crests  is  apparent  in  the  curves,  corresponding  to  the  com- 
plexity of  structure  which  these  bands  show  when  the  substance  is 
excited  at  the  temperature  of  liquid  air.  The  vertical  lines  indicate 
the  position  of  the  bands,  as  observed  at  low  temperatures  by  methods 
to  be  described  in  subsequent  chapters. 
That  these  lines  in  general  do  not  co- 
incide with  the  positions  of  the  crests 
might  seem  to  indicate  that  there  is  no 
definite  relation  between  the  spectra  at 
the  two  temperatures  or  that  the  accu- 
racy of  the  curves  is  in  doubt;  but  the 
discrepancies  are  quite  in  accordance 
with  the  results  obtained  by  the  detailed 
study  of  the  spectra  of  the  double 
chlorides  (Chapter  V),  where  the  spectra 
are  sufficiently  resolved  at  +20°  C.  to 
enable  us  to  trace  the  changes  on  cool- 
ing, measure  the  definite  shifts,  and  dis- 
cover the  remarkable  mechanism  of  the 
process  of  resolution.  ^     , , 

Fig.  14. 


24 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


EXCITATION  BY  LIGHT  OF  DIFFERENT  WAVE-LENGTHS. 

y 

If  all  the  bands  of  the  luminescence  spectrum  are  due  to  the  vibra- 
tions of  a  single  connected  system  it  would  be  natural  to  expect  that 
an  agency  which  excited  one  would  also  excite  the  rest,  especially  if 
luminescence  is  due  to  the  recombination  of  ions  dissociated  by  the 
exciting  Hght,  or  to  the  return  of  an  electron  set  free  by  the  exciting 


agency.  On  the  other  hand,  if  each  band 
is  dne  to  some  process  going  on  in  one 
particular  compound  or  molecular  aggre- 
gation, wave-lengths  might  be  found 
which  would  excite  one  band  and  not  the 
rest,  or  which  would  at  any  rate  excite 
the  bands  in  different  degree. 

To  test  this  matter  we  have  measured 
the  distribution  of  intensity  in  the  bands 
for  excitation  by  different  lines  in  the 
ultra-violet  spectrum  of  the  quartz 
mercury  lamp.  The  intensity  of  fluo- 
rescence with  this  excitation  is  not  suffi- 
cient to  permit  the  measurement  of,  all 
the  bands,  so  that  the  three  brightest 
bands  only  have  been  measured.  In 
table  11  the  intensities  for  excitation  by  the  different  lines  in  the  mer- 
cury spectrum  are  given  for  five  different  uranyl  salts.  Curves  show- 
ing the  variation  of  the  relative  intensity  with  the  wave-length  of  the 
exciting  light  are  shown  for  uranyl-nitrate  crystals  in  figure  18,  and  for 
the  double  sulphate  in  figure  19.  In  each  case  the  intensity  of  the 
most  intense  band  has  been  put  equal  to  10.  The  variation  was 
greater  in  the  case  of  the  double  sulphate  than  in  the  case  of  any  other 
gait  studied.  The  observations  were  repeated  in  the  case  of  this  sub- 
stance on  two  different  days  and  a  comparison  of  the  full  and  dotted 


I 

aojoo 

JJ 

•  •|90         '■ 

f 

\ 

—20 

\ 

\ 

—15 

/ 

li 

\ 

—10 

\ 

1 

1     1 

1                           1               ^ 

.50  .51^ 

Fig.  17. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      25 


curves  indicates  the  extent  to  which  the  results  agree.  In  the  case  of 
the  other  salts  studied,  curves  very  similar  to  that  of  figure  18  were 
obtained. 


Table  11.— Relative  intensity  of  excitation  of  the  three  brightest  bands  by  five  different  lines 

in  the  spectrum  of  the  mercury  arc. 

Wave- 

Intensity^ of  luminescence 

1 

length  of 

at  crest. 

Ratio 
a/b. 

Ratio 
c/b. 

exciting 

light. 

Band  a. 

Band  b. 

Band  c. 

Uranyl-potassium  sulphate: 

0.436AI 

12.5 

22.7 

7.45 

0.55 

0.33 

.407 

12.6 

26.4 

8.45 

.48 

.32 

Band  a 4,920 

.366 

10.5 

23.2 

6.65 

.45 

.29 

b 5,130 

.313 

16.25 

22.9 

8.27 

.71 

.36 

c 5,360 

.254 

8.83 

13.9 

4.25 

.64 

.31 

Uranyl  phosphate: 

.436)u 

10.0 

10.2 

3.07 

.98 

.30 

.407 

6.04 

6.06 

1.90 

1.00 

.31 

Band  a 5,015 

.366 
.313 

9.7 
11.1 

9.7 
10.4 

2.47 
3.04 

1.00 
1.07 

.25 
.29 

b 5,239 

c 5,483 

.254 

6.85 

5.35 

1.28 

Uranyl  nitrate  (anhydrous) : 

.436)u 

22.9 

38.7 

15.5 

.59 

.41 

.407 

15.3 

22.7 

9.30 

.67 

.41 

Band  a 4,849 

.366 

15.3 

20.7 

8.87 

.47 

.43 

b 5,071 

.313 

21.8 

31.6 

11.7 

.69 

.37 

c 5,311 

.254 
.436m 

6.0 
18.6 

7.7 
27.2 

3.2 
10.0 

.78 
.69 

.42 
.37 

Uranyl  nitrate  (crystals) : 

.407 

17.5 

24.5 

8.6 

.73 

.35 

Band  a 4,869 

.366 

12.2 

18.3 

7.5 

.67 

.41 

b 5,086 

.313 

17.3 

25.6 

9.6 

.67 

.38 

c 5,329 

.254 

8.3 

10.5 

4.0 

.79 

.38 

Uranyl  fluorid  fluor- ammonium: 

.436/i 

10.3 

11.2 

3.7 

.92 

.33 

.407 

23.3 

25.0 

7.7 

.93 

.37 

Band  a 5,008 

.366 

20.4 

25.7 

7.6 

.79 

.30 

b 5,237 

.313 

37.5 

43.4 

11.5 

.87 

.27 

c 5,460 

.254 

15.8 

17.6 

5.7 

.90 

.32 

^The  intensities  given  in  table  11  are  not  corrected  for  energy  distribution  in  the  acetylene  flame. 

It  will  be  noticed  that  the  lower  curve  in  figures  18  and  19  indicates 
a  very  nearly  constant  ratio  between  the  intensity  of  the  brightest 
band  and  that  of  the  band  lying  next  in  the  direction  of  the  red.  But  if 
we  compare  the  brightest  band  with  the  band  lying  next  to  the  violet 
side  we  find  a  considerable  variation  intheratio  of  intensities,  especially 
in  the  case  of  the  double  sulphate.  It  appears  to  us  probable  that  this 
variation  is  the  result  of  a  partial  absorption  of  the  luminescence  by  the 
substance.  The  absorbing  power  of  a  given  salt  differs  for  the  different 
mercury  lines  used,  so  that  in  some  cases  the  exciting  light  may  pene- 
trate much  further  into  the  substance  than  in  others.  It  is  clear  that 
those  bands  for  which  the  absorption  is  greatest  will  appear  relatively 
weaker  when  the  exciting  light  penetrates  a  considerable  distance  into 
the  substance,  even  if  the  relative  intensity  of  the  excitation  of  the 
different  bands  is  really  the  same  for  all  wave-lengths  of  the  exciting 


26 


FLUORESCENCE   OF   THE   URANYL   SALTS. 


light.  The  observed  distribution  of  energy  would  correspond  with  the 
actual  distribution  only  in  case  an  excessively  thin  layer  of  the  sub- 
stance is  excited — so  thin  that  the  absorption  of  the  light  emitted  is  neg- 
ligible. As  a  matter  of  fact,  the  band  lying  to  the  violet  side  of  the 
maximum  is  in  a  region  where  the  absorption  is  considerable,  while 
the  brightest  band  and  those  lying  to  the  red  are  in  the  region  where 
the  absorption  is  small.  The  constancy  of  the  ratio  in  the  case  of  the 
lower  curves,  and  the  small  variation  of  the  ratio  shown  by  the  upper 
curves,  are  therefore  entirely  consistent  with  the  view  that  the  observed 
variations  are  the  result  of  absorption,  and  that  the  first  effect  of 
excitation,  whatever  may  be  the  wave-length  of  the  exciting  Hght,  is 
to  produce  all  of  the  bands  with  a  definite  and  constant  intensity 
distribution. 


^ 

9 

c 

4 

-^--^ 

4 

V::?^ 

? 

2   ~ 

^•~=*^ 

.30 

1 

A^M 

•? 

.40  /^ 

Fig.  18. 


Fig.  19. 


Relative  intensities  of  the  brightest  fluorescence  bands  of  uranyl  nitrate  (fig.  18)  and  uranyl- 
potassium  sulphate  (fig.  19).  The  intensity  of  the  brightest  band  is  put  equal  to  10.  The  upper 
curve  in  each  figure  refers  to  the  band  lying  next  to  the  brightest  toward  the  violet.  The  lower 
curve  refers  to  the  band  toward  the  red.  Abscissae  give  the  wave-length  of  the  exciting  light. 
(See  table  11.) 

The  observations  recorded  in  the  foregoing  paragraphs  all  tend  to 
indicate  that  the  fluorescence  spectrum  of  a  uranyl  salt  is  a  homo- 
geneous complex. 

The  envelope  is  single-crested  and  has  the  form  typical  of  a  simple 
band.  Neither  its  position  nor  form  is  modified  by  changing  the  mode 
of  excitation.  To  test  this  conclusion  we  have  made  many  experiments 
under  widely  varying  conditions,  especially  in  the  way  of  selective  and 
monochromatic  excitation  of  the  resolved  spectra,  where  it  should  be 
possible  to  observe  critically  the  disappearance  or  enhancement  of 
single  narrow  components  of  groups  of  series. 

The  remarkable  effects  of  selective  excitation  recorded  by  Wood  in 
the  case  of  fluorescent  vapors  might  lead  to  the  expectation  of  similar 
or  analogous  changes  in  the  uranyl  spectra.  All  these  attempts  have 
thus  far  been  without  result,  and  we*are  inclined,  therefore,  to  regard 
the  spectrum  as  a  unit  and  to  consider  it  as  a  broad,  simple  band,  which 
unlike  the  other  bands  of  this  type  as  yet  discovered,  consists  of 
resolved  instead  of  completely  overlapping  components. 

Studies  to  be  described  in  Chapter  IV  are  in  confirmation  of  this 
view  in  that  the  criterion  for  a  simple  band,  based  upon  the  phenomena 
of  phosphorescence,  is  fulfilled. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      27 


THE  ABSORPTION  SPECTRUM  AT  ORDINARY  TEMPERATURES. 

The  resemblance  of  the  absorption  spectra  of  the  uranyl  salts  to  their 
fluorescence  spectra,  which  is  so  striking  as  to  have  led  both  E.  and  H. 
Becquerel  to  regard  the  absorption  series  as  a  continuation  of  the  series 
of  fluorescence  bands,  can  be  fully  investigated  only  by  observations 
at  low  temperatures.  Since  the  absorption  extends  into  the  ultra- 
violet, moreover,  photographic  methods  are  necessary.  The  study  of 
the  absorption  at  ordinary  temperatures  is,  however,  not  without  sig- 
nificance, and  the  use  of  the  spectrophotometer  in  this  work  brings  out 
certain  features  not  easily  discernible  in  the  photographic  plates. 

The  salts  thus  studied  by  us 
were  in  powdered  form  and  the 
location,  relative  intensity,and 
character  of  the  bands  lying 
within  the  visible  spectrum 
were  determined  by  measur- 
ing the  intensity  of  the  light 
transmitted  by  an  extremely 
thin  layer  between  glass  plates, 
or  in  some  instances  by  ob- 
serving the  spectrum  of  white 
light  reflected  from  the  surface 
of  the  powder.  Recourse  to 
the  latter  method  is,  indeed, 
frequently  necessary  because 
of  the  great  and  rapidly  in- 
creasing opacity  of  these  sub- 
stances in  the  blue  and  violet. 

The  nature  of  the  results  of 
such  measurements  is  suffi- 
ciently shown  in  figure  20, 
which  is  plotted  from  deter- 
minations of  the  light  transmitted  by  a  thin  layer  of  uranyl  potassium 
sulphate.     The  source  of  light  was  an  acetylene  flame. 

The  measurements  cover  not  only  a  considerable  portion  of  the 
absorbing  region,  but  also  a  part  of  the  region  containing  the  fluores- 
cence bands.  Three  of  these  bands  show  very  clearly,  even  when 
superposed  upon  the  brilliant  continuous  spectrum  of  the  acetylene 
flame.  The  absorption  begins  a  little  on  the  violet  side  of  the  brightest 
luminescence  band  and  extends  into  the  ultra-violet.  It  will  be  noticed 
that  there  are  several  definite  and  narrow  absorption  bands,  which 
appear  to  be  superposed  upon  a  broad  band,  or  region,  of  general 
absorption.  This  appearance  of  a  broad  band  might  result  from  the 
overlapping  of  the  group  of  narrow  absorption  bands,  only  the  crests 
of  which  can  be  observed.     In  estimating  the  relative  intensity  of  the 


Fig.  20. — Transmission  of  a  thin  layer  of  uranyl- 
potassium  sulphate,  showing  absorption  bands 
and  three  of  the  fluorescence  bands.  Curves  F 
and  A  show  the  relative  intensities  of  the  bands 
of  fluorescence  and  absorption  respectively. 


28  FLUORESCENCE    OF   THE    URANYL    SALTS. 

absorption  bands  we  have  adopted  the  first  view  and  have  assumed  a 
general  absorption^  such  as  is  indicated  by  the  dotted  Une  of  figure  20. 
The  deviations  from  this  dotted  curve  have  been  ascribed  to  the  effect 
of  the  narrow  bands.  The  intensity  of  each  band  is  determined  by 
taking  the  ratio  of  the  diminution  of  the  transmission  which  it  produces 
to  the  transmission  which  would  be  expected  if  the  general  absorption 
only  were  present. 

Both  the  absorption  bands  and  the  fluorescence  bands  have  been 
indicated  in  figure  20  by  lines  whose  lengths  are  proportional  to  the 
intensities  of  the  bands.  If  a  Une  is  drawn  through  the  ends  of  the 
lines  that  give  the  intensity  of  the  absorption  bands  a  curve  (A)  is 
obtained  which  is  very  similar  in  form  to  the  absorption  curve  for  a 
substance  having  a  single  broad  band.  This  curve  also  has  the  same 
position  with  reference  to  the  envelope  of  the  luminescence  bands  (F) 
that  the  absorption  curve  in  such  cases  has  to  the  luminescence  curve. 
It  appears  highly  probable  that  just  as  a  broad  luminescence  band  may 
result  from  the  overlapping  of  a  group  of  bands,  so  the  absorption  of 
the  same  substance  may  result  from  the  overlapping  of  a  similar  group 
of  absorption  bands. 

The  transmission  curve  for  a  thin  layer  of  powdered  uranyl  sulphate 
is  shown  in  figure  21,  the  source  of  light  being  an  acetylene  flame.  In 
its  general  features  this  curve  is  similar  to  that  for  the  double  sulphate 
of  uranyl  and  potassium.  The  fluorescence  of  the  sulphate  is  not  so 
brilliant  and  the  fluorescence  bands  therefore  show  less  prominently. 
The  sulphate,  as  has  been  shown  in  a  preceding  paragraph,  has  the 
peculiarity  of  possessing  two  series  of  fluorescence  bands  lying  close 
together,  one  set  of  bands  being  much  more  intense  than  the  other. 
It  will  be  noticed  that  the  absorbed  bands  are  also  double.  If  we  think 
of  the  more  intense  luminescence  bands  as  constituting  the  principal 
series  and  the  less  intense  bands  forming  a  secondary  series,  a  curious 
reversal  is  noticeable  as  we  pass  from  the  region  of  fluorescence  to  the 
region  of  absorption.  Each  band  of  the  principal  series  in  the  lumines- 
cence region  lies  a  little  to  the  right  of  the  corresponding  band  of  the 
secondary  series.  The  positions  of  the  bands  are  indicated  by  short 
vertical  lines  in  the  lower  part  of  figure  21,  the  bands  of  the  secondary 
series  being  represented  by  dotted  lines.  When  we  pass  to  the  absorp- 
tion series,  however,  the  more  intense  band  lies  to  the  left  in  each  case. 
For  example,  the  absorption  band  at  4,925  corresponds  in  position  with 
a  fluorescence  band  of  the  principal  series;  but  the  absorption  band  at 
4,880,  which  probably  corresponds  to  the  band  4,890  of  the  secondary 
fluorescence  series,  is  by  far  the  more  intense  of  the  two. 

^  The  fact  that  all  the  uranyl  salts,  so  far  as  known,  increase  rapidly  in  opacity  as  the  wave- 
length of  the  transmitted  light  decreases,  even  when  the  bands  are  greatly  reduced  in  width  by 
cooling,  seems  conclusive  as  to  this  assumption. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      29 


It  will  be  observed  that  the  absorption  bands  of  uranyl  potassium 
sulphate  occurring  at  4,760  and  4,920  (fig.  20)  appear  to  coincide  in 
position  with  two  of  the  luminescence  bands  of  the  same  substance.  In 
other  words,  these  two  bands  are  ^' reversible'^  and  may  appear  either 
as  absorption  bands  or  as  luminescence  bands,  according  to  the  con- 
ditions under  which  they  are  observed.  The  double  sulphate  thus 
shows  the  same  phenomenon  that  was  first  described  by  H.  Becquerel^ 
in  1885  in  the  case  of  uranyl  nitrate. 


A 

/ 

/       ^ 

\ 

/VA/- 

\ 

10 

f 

V 

I 

\ 

V 

(\ 

5 

/^ 

/ 

f' 

y 

i 

J 

\  1 

1 

1 

1 1 

1 

1 

1 

:l 

Fig.  21. 


.50  .55, 

-Transmission  of  a  thin  layer  of  uranyl  sulphate. 


It  was,  however,  of  interest  to  study  these  relations  in  the  case  of 
the  uranyl  spectra  at  ordinary  temperatures  also.  Special  precautions 
were  necessary,  for  when  a  luminescence  band  occurs  in  a  region  where 
there  is  appreciable  absorption  it  is  clear  that  the  apparent  position  of 
the  crest  of  the  band  may  be  influenced  by  absorption  in  case  the  latter 
is  not  uniform.  Where  measurements  of  absorption  are  made  with 
light  containing  rays  that  are  capable  of  exciting  fluorescence  there 
m^y  also  be  a  displacement  of  the  crest  of  the  absorption  band,  owing 
to  the  presence  of  luminescence.     There  could  be  no  displacement  of 

1  Comptes  Rendus,  vol.  101,  p.  1252.     1885. 


30  FLUORESCENCE    OF   THE   URANYL   SALTS. 

this  sort  in  case  the  light  emitted  were  strictly  proportional  to  the 
coefficient  of  absorption;  but  if  the  fluorescence  band  and  the  absorp- 
tion band  do  not  exactly  coincide  in  position  or  in  form,  such  a  dis- 
placement is  to  be  expected. 

In  order  to  avoid  the  necessity  of  changing  the  adjustment  of  the 
spectrophotometer,  or  the  position  of  the  substance,  between  measure- 
ments a  thin  layer  of  the  uranyl  potassium  sulphate  was  in  some  cases 
mounted  permanently  in  front  of  the  slit.  To  locate  the  absorption 
bands  the  slit  was  illuminated,  through  the  specimen,  with  light  from  an 
acetylene  flame.  To  observe  the  luminescence  bands  a  piece  of  blue 
glass  was  placed  in  front  of  the  flame,  so  as  to  cut  off  the  rays  having 
the  same  wave-length  as  the  bands,  while  permitting  the  exciting  rays 
to  pass;  or  in  some  cases  the  acetylene  flame  was  replaced  by  a  mercury 
arc.  To  guard  against  the  presence  of  fluorescence  in  measurements 
of  absorption  a  green  glass  was  sometimes  used. 

With  the  relatively  thick  specimen  first  used  the  absorption  was  so 
great  that  the  band  at  4,760  could  not  be  observed.  The  band  at  4,920 
was  well  defined,  however,  and  could  be  accurately  located.  If  the 
eyepiece  pointer  was  set  at  the  crest  of  the  absorption  band  and  the 
source  of  light  then  changed  so  as  to  bring  out  the  fluorescence  band, 
the  latter  was  seen  to  be  very  obviously  displaced  toward  the  red. 
Photographs  of  the  absorption  and  fluorescence  spectra  taken  on  the 
same  plate  also  showed  the  relative  displacement  of  the  two  bands  very 
clearly.  The  wave-length  of  the  fluorescence  band  as  measured  under 
these  conditions  was  not  the  same,  however,  as  that  previously  deter- 
mined, and  the  whole  appearance  of  the  band  was  different  from  what 
had  been  observed  when  looking  at  the  front  surface  of  the  luminescent 
substance. 

More  definite  conditions  for  observing  the  absorption  band  were 
obtained  by  using  nearly  monochromatic  light  for  transmission  meas- 
urements. The  spectrum  of  a  Nernst  glower  was  formed  by  a  large 
spectrometer  and  a  small  region  of  the  spectrum  was  isolated  by  means 
of  a  suitable  screen  containing  a  slit.  The  light  coming  through  this 
slit,  after  passing  through  the  specimen  to  be  studied,  fell  upon  the  slit 
of  the  spectrophotometer.  By  suitable  adjustment  the  center  of  the 
band  of  transmitted  light  could  be  made  practically  coincident  with 
the  center  of  the  absorption  band  and  the  latter  could  be  located  with 
considerable  accuracy.  Under  these  circumstances  the  transmitted 
light  contained  no  rays  capable  of  exciting  any  observable  fluorescence, 
so  that  we  may  look  upon  the  determinations  of  absorption  by  this 
method  as  uninfluenced  by  errors  due  to  the  presence  of  luminescence. 

Using  a  relatively  thick  layer,  the  absorption  band  was  located  at 
4,919,  while  the  crest  of  the  fluorescence  band  (observed  by  transmis- 
sion) lay  at  4,974.  An  excessively  thin  layer,  formed  by  depositing 
the  salt  from  a  solution,  or  suspension,  in  alcohol,  gave  a  fluorescence 


( 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      31 

band  whose  crest  was  at  4,925,  while  the  wave-length  of  the  very  faint 
absorption  band  was  4,922.  Our  previous  determination  of  the  wave- 
length of  the  luminescence  band,  when  looking  at  the  surface  exposed 
to  the  exciting  rays,  was  4,920.  These  results  appear  to  us  to  warrant 
the  conclusion  that  if  disturbances  due  to  absorption  could  be  entirely 
eliminated  the  two  bands  would  be  found  to  have  exactly  .the  same 
wave-length. 

It  must  not  be  forgotten,  however,  that  it  is  nearly  impossible  to 
observe  the  fluorescence  spectrum  under  conditions  which  entirely 
eliminate  effects  due  to  absorption.  The  exciting  light  always  pene- 
trates to  some  extent  beneath  the  surface,  so  that  some  of  the  emitted 
Hght  must  pass  through  the  fluorescent  material  before  it  can  reach 
the  eye.  It  is  natural,  therefore,  to  expect  a  slight  displacement  in  all 
cases.  Although  our  most  reliable  measurement  of  the  wave-length 
of  the  absorption  band,  4,919,  and  our  best  determination  of  the  crest 
of  the  luminescence  band,  4,920,  differ  by  less  than  the  probable  errors 
of  measurement,  we  feel  that  it  is  not  unlikely  that  the  difference  is  a 
real  one,  due  to  the  cause  just  cited. 

The  absorption  band  at  4,760  in  the  double  sulphate  differs  in  posi- 
tion by  5  units  from  the  fluorescence  band  at  4,765.  A  portion  of  this 
difference  may  also  be  explained  by  absorption.  But  it  is  probably 
chiefly  due  to  the  difficulty  in  accurately  locating  the  crests  of  these 
bands.  The  fluorescence  band  is  extremely  faint,  while  the  absorption 
band  is  not  very  sharp,  because  of  the  large  general  absorption  in  this 
region. 

Using  a  thick  layer,  formed  by  grinding  down  a  translucent  mass  of 
adhering  crystals  until  a  piece  about  0.5  mm.  thick  was  obtained,  a 
faint  absorption  band  was  observed  at  5,127.  This  corresponds  to  the 
brilliant  fluorescence  band  at  5,130.  In  all  likelihood  the  coincidence 
here  is  complete,  since  measurements  of  the  fluorescence  band  made  at 
the  same  time  and  with  the  same  specimen  as  that  used  for  absorption 
measurements  gave  the  same  wave-length,  5,127,  for  both  bands. 

EXCITATION  BY  LIGHT  CORRESPONDING  TO  DIFFERENT  PARTS 
OF  THE  ABSORPTION  REGION. 

It  seemed  a  matter  of  some  interest  to  determine  the  relative  effec- 
tiveness of  light  of  different  wave-lengths  in  producing  fluorescence, 
and  experiments  having  this  end  in  view  have  been  made  in  the  case  of 
the  double  sulphate.  We  were  particularly  interested  in  determining 
whether  wave-lengths  falling  within  the  sharp  absorption  bands  at 
4,918,  4,760,  4,615,  etc.,  were  especially  effective  in  exciting  lumines- 
cence. 

The  source  of  the  exciting  light  used  in  these  experiments  was  a  Nernst 
glower  which  was  mounted  in  place  of  the  slit  of  a  spectrometer.  The 
spectrum  was  f  ocussed  upon  an  opaque  screen  containing  a  narrow  slit, 
and  the  light  passing  through  this  slit  was  used  in  exciting  the  speci- 


32 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


men  tested.  The  fluorescence  spectrum  was  observed  in  a  spectro- 
photometer, the  specimen  being  set  up  at  an  angle  of  approximately 
45^  with  the  path  of  the  exciting  light,  so  that  the  collimator  of  the 
spectrophotometer  could  be  pointed  at  the  illuminated  surface  without 
interfering  with  the  exciting"  light.  Enough  of  the  exciting  rays  were 
reflected  into  the  spectrophotometer  to 
enable  the  range  of  wave-lengths  used 
in  each  case  to  be  determined.  The 
spectrophotometer  was  then  set  at  the 
crest  of  the  principal  fluorescence  band 
and  the  intensity  measured  by  com- 
parison with  an  acetylene  standard. 
Observations  of  this  sort  were  repeated 
throughout  the  absorbing  region.  The 
results  are  shown  in  figure  22.  It  will  be 
noticed  that  the  regions  of  strong  excita- 
tion at  4,910  and  4,775  correspond  very 
closely  to  the  two  absorption  bands  at 
4,920  and  4,766.  Some  slight  indication 
is  also  present  of  the  other  absorption 
bands.  It  is  clear,  however,  that  the 
ability  to  excite  luminescence  is  not  con- 
fined to  rays  falling  within  the  narrow 
absorption  bands,  but  extends  to  the 
region  of  general  absorption  lying  be- 
tween. It  is  not  possible  to  determine 
the  specific  exciting  power  of  different 
rays,  as  has  been  done  in  the  case  of  eosin 
and  resorufin,^  because  of  our  ignorance 
of  the  absorbing  power  of  the  salt  for 
different  wave-lengths.^  The  results  indicate,  however,  that  the  specific 
exciting  power  varies  only  slightly  with' the  wave-length,  as  in  the  case 
of  resorufin  and  eosin. 

THE  RELATION  BETWEEN  ABSORPTION  AND  FLUORESCENCE  AS 
IT  APPEARS  AT  ORDINARY  TEMPERATURES. 

In  1885  H.  BecquereP  made  measurements  of  the  spectrum  of  uranyl 
nitrate  from  which  it  would  appear  that  the  frequency  interval  remains 
constant  in  passing  from  the  fluorescence  to  the  absorption  spectrum 
and  that  the  suggestion  of  E.  Becquerel  in  his  classical  memoir  of  1872, 
that  the  emission  bands  and  absorption  bands  belong  to  the  same  series, 
is  in  accordance  with  the  facts. 

H.  Becquerel  also  showed  that  two  of  the  bands  are  reversible,  ap- 
pearing as  emission  bands  when  suitably  excited,  whereas  if  light  free 

^  Physical  Review,  xxxi,  p.  381. 

'  The  distribution  of  energy  in  the  spectrum  of  the  Nernst  glower  also  has  not  been  determined. 

•  H.  Becquerel,  Comptes  Rendus,  101,  p.  1252. 


-TO 

-/— 


1 
1 


.4  2 


.46 


50/* 


Fig.  22. — Intensity  of  fluorescence 
(ordinates)  produced  by  exciting 
light  of  different  wave-length  (ab- 
). 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      33 


from  exciting  rays  be  passed  through  the  substance,  absorption  bands 
in  the  same  location  are  observed. 

In  our  own  work  upon  uranyl  nitrate  and  potassium  uranyl  sulphate 
we  have  confirmed  the  results  of  H.  Becquerel  so  far  as  the  existence 
of  reversible  bands  is  concerned  and  have  found  for  these  substances 
3  such  bands  instead  of  2. 

The  frequency  interval  between  absorption  bands,  like  the  fluores- 
cence interval,  is  approximately  constant,  but,  as  may  be  seen  from 
tables  12  and  13,  it  is  much  smaller. 

Additional  evidence  on  this  point  will  be  found  in  the  chapters 
dealing  with  the  double  chlorides  and  with  the  spectra  at  low  tempera- 
tures, where  it  will  be  established  as  a  relation  common  to  all  uranyl 
spectra.  The  study  of  the  absorption  spectra  at  +20°  C.  is  uncertain 
and  unsatisfactory,  because  we  have  to  do  with  unresolved  groups  of 
bands,  and  these  two  examples  will  suffice  to  illustrate  the  remarkable 
way  in  which  the  two  frequencies  interlock  where  fluorescence  goes 
over  into  absorption. 

Table  12. — Absorption  and  fluorescence  bands  of  potassium  uranyl  sulphate  at  +20°  C. 


Absorption. 

Fluorescence. 

M- 

1/mX103. 

Interval. 

M- 

1/mX102. 

Interval. 

0.4350 

2298.9 

62.8 

.4472 

2236.1 

68.8 

.4614 

2167.3 

66.5 

.4760 

2100.8 

68.3 

0.4765 

2098.6 

66.1 

.4920 

2032.5 

82.0 

.4920 

2032.5 

83.2 

.5127 

1950.5 

.5130 
.5360 
.5606 
.5881 
.6190 

1949.3 
1865.7 
1783.8 
1700.4 
1615.5 

83.6 
81.9 
83.4 
84.9 

It  will  be  seen  from  tables  12  and  13  that  the  last  3  fluorescence 
bands,  counting  from  the  red,  are  nearly  or  quite  coincident  with  the 
first  three  absorption  bands.  Whether  or  not  these  coincidences  are 
to  be  regarded  as  exact  can  not  be  determined  from  observations  on 
unresolved  spectra.  It  will  be  demonstrated  later  that  reversals  are 
exact  between  the  ultimate  components  of  bands,  but  not,  in  general, 
between  unresolved  aggregates. 

That  the  fluorescence  interval  changes  to  conform  to  the  absorption 
interval  at  the  last  step  appears  not  only  from  the  data  in  tables  12 


34 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


and  13,  but  also  in  the  determinations  for  other  salts  (tables  4  to  10) 
wherever  the  final  fluorescence  band  (8)  has  been  observed.  The 
corresponding  change  in  the  absorption  interval  to  conform  with  the 
fluorescence  interval  is  much  more  difficult  to  estabhsh,  because  the 
last  absorption  band  toward  the  red  is  entirely  invisible  under  ordinary- 
conditions. 

Table  13. — Absorption  and  fluorescence  hands  of  uranyl  nitrate  at  -\-20°  C. 


Absorption  bands.  ^ 

Fluorescence  bands. 

M- 

1/mX103. 

Interval. 

fX. 

1/fxXlOK 

Interval. 

0.3830 

2610.9 

69.6 

.3935 

2541.3 

72.2 

.4050 

2469.1 

71.0 

.4170 

2398.1 

58.9 

.4275 

2339.2 

69.1 

.4405 

2270.1 

72.3 

.4550 

2197.8 

71.9 

.4705 

2125.4 

72.0 

0.4708 

2124.0 

70.2 

.4870 

2053.4 

87.2 

.4869 

2053.8 

86.6 

.5086 

1966.2 

.5086 

.5329 
.5585 
.5866 
.6188 

1966.2 
1876.5 
1790.5 
1704.7 
1616.0 

89.7 
86.0 

85.8 
88.7 

I 


^  Absorption  bands,  excepting  that  at  0.5086  are  from  measurements 
by  Jones  and  Strong  (Am.  Chem.  Journal,  1910). 

EFFECT  OF  WATER  OF  CRYSTALLIZATION— BEHAVIOR  OF  SOLUTIONS. 

The  effects  of  water  of  crystallization  and  the  comparison  of  the 
spectra  of  the  solid  uranyl  compounds  with  those  of  their  solutions  are 
to  be  treated  at  some  length  in  subsequent  chapters.  A  few  points 
which  have  been  brought  out  in  the  course  of  our  work  on  the  spectra 
at  +20°  C.  are,  however,  recorded  here. 

The  effect  of  water  of  crystallization  in  the  case  of  uranyl  nitrate  is 
to  shift  the  luminescence  bands  slightly  in  the  direction  of  the  longer 
waves.  (Compare  the  hexahydrate  with  the  anhydrous  form  in  table 
1.)  This  is  the  effect  which  it  would  seem  most  natural  to  expect,  since 
the  mass  of  the  vibrating  system  is  increased  by  the  addition  of  water  of 
crystallization  without  any  increase,  so  far  as  we  know,  in  the  elastic 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      35 


/S'a'     fi*.'     tS'oL 
1  1.        tl   .      !  1     . 

,     ,r    ,r   .  r  ,   T,     , 

.     .  ,  .    1.     1.     .     . 

,1,1 

.46 

Fia.  23. 


.58^ 

-Position  of  fluorescence  and  absorption 
bands  of  uranyl  sulphate. 


forces  of  the  system.  In  fact,  the  presence  of  water  so  intimately 
associated  with  the  salt  molecule  would  probably  increase  the  effective 
dielectric  constant  of  the  region  in  which  the  vibrations  occur,  and 
would  thus  cause  a  decrease  in  frequency  quite  independent  of  any 
effect  due  to  increase  in  mass. 

It  has  been  shown  by  Deusen^  and  by  Jones  and  Strong'  that  the 
absorption  spectrum  of  the  crystaUized  nitrate  is  nearly  coincident  with 
the  absorption  spectrum  of  the  aqueous  solution.  In  many  cases  no 
difference  can  be  detected  in  the 
wave-length  of  the  band  in  solu- 
tion and  in  the  solid  crystal.  In 
the  case  of  other  bands,  however, 
the  difference  appears  to  be  too 
great  to  be  accidental.  It  seems 
not  unlikely  that  the  absorption 
spectrum  contains  several  series 
of  bands,  some  of  which  occupy 
almost  identically  the  same  po- 
sitions for  the  solution  as  for  the 
solid  salt.  We  must  assume,  therefore,  that  at  least  a  part  of  the 
dissolved  salt  has  the  same  molecular  structure  as  the  solid  crystals. 

In  the  case  of  the  uranyl  sulphate  studied  by  us  the  phenomena  are 
more  complicated.  As  has  already  been  shown,  the  luminescence 
spectrum  of  this  salt,  even  at  ordinary  temperatures,  contains  two 
series  of  bands,  which  for  convenience  we  shall  designate  the  a  and  /3 
series  respectively.  The  a  bands  are  by  far  the  stronger  and  6  of  these 
could  be  observed.  Of  the  relatively  weak  ^  bands  only  3  could  be 
seen.  In  the  absorption  spectrum  of  the  solid  salt  2  series  of  bands 
were  also  found  (see  fig.  21)  which  we  shall  call  the  a'  and  j3'  bands. 
Two  of  the  (x!  bands  corresponded  in  position  with  two  of  the  a  bands 
of  luminescence,  while  one  band  of  the  ^'  series  corresponded  with  one 
of  the  /3  bands.  The  wave-lengths  are  given  in  table  14  and  are  shown 
graphically  in  figure  23.     It  is  a  remarkable  fact  that  while  the  a  bands 

Table  14. — Uranyl  sulphate  fluorescence  and  absorption  bands. 

Fluorescence: 

Crystals— Principal  series  (a) 4763  4929  5148         5395         5659         6926 

Crystals— Secondary  series  (/3) 4894  5098 

Dehydrated  salt  (7) 4843  5049 

Concentrated  solution 4928  5145 

Absorption : 

Crystals — a'  series 4595  4755  4925 

Crystals— /3'  series 4555  4720  4880 

Concentrated  solution 4718  4887         5095 


5395 
5340 
5285 
5387 


5538 


^  Annalen  der  Physik,  43,  p.  1128.     1898. 
"  American  Chemical  Journal,  vol.  xliii,  p.  37,  1910. 
1889. 


See  also  Vogel,  Spectralanalyse,  p.  270, 


36 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


are  much  the  brighter  in  the  luminescence  spectrum,  the  a'  bands  in 
the  absorption  spectrum  are  much  weaker  than  the  jS'  bands. 

The  sulphate  used  in  this  experiment  was  in  the  form  of  small  crystals, 
When  the  salt  was  dehydrated  by  being  kept  for  about  an  hour  in  a 
stream  of  warm,  dry  air  its  luminescence  spectrum  was  found  to  be 
absolutely  different,  each  band  being  shifted 
toward  the  violet  by  about  100  A.  u.  Brief 
exposure  to  the  air  apparently  permitted  a 
portion  of  the  salt  to  return  to  the  original 
condition,  so  that  the  original  a  andjS  bands 
could  be  seen  as  well  as  the  y  bands  charac- 
teristic of  the  dehydrated  salt.  In  the  case 
of  a  thin  layer  of  the  sulphate  which  had 
been  dehydrated  and  then  exposed  for  a 
short  time  to  the  air,  each  of  the  lumi- 
nescence bands  was  found  to  consist  of 
three  overlapping  bands,  the  components 
corresponding  in  position  to  the  a,  /?,  and 
7  bands  respectively.  Spectrophotometric 
measurements  (with  a  rather  wide  slit)  of 
the  brightest  luminescence  band  and  of  a 
portion  of  the  absorption  spectrum  of  the 
same  layer  are  shown  in  figure  24.  In  the 
luminescence  spectrum  the  /3  bands  are  by 
far  the  most  prominent,^  while  in  the  ab- 
sorption spectrum  the  a'  bands  are  strong- 
est and  no  y'  bands  can  be  detected.  The 
results  point  to  the  existence  of  two  dif- 
ferent hydrated  salts  corresponding  to  the 
a  and  fi  bands  respectively,  but  further 
study  would  be  necessary  to  make  possible 
an  entirely  satisfactory  explanation  of  the 
observed  phenomena. 

The  concentrated  aqueous  solution  of  the  sulphate  showed  weak  fluor- 
escence, and  the  three  brightest  bands,  which  could  be  located  with 
reasonable  accuracy,  were  found  to  agree  in  position  with  three  of  the 
a  bands  of  the  solid  crystallized  salt.  In  the  absorption  spectrum  of 
the  concentrated  solution  it  was  possible  to  locate  three  well-defined 
bands,  two  of  which  corresponded  with  two  of  the  fi  bands  of  the  solid 
salt  (see  fig.  25).  The  solution  showed  no  trace  of  any  fluorescence 
corresponding  to  the  /?  series,  nor  did  it  show  any  trace  of  absorption 
corresponding  to  the  a'  series. 

^  The  a'  band  appears  in  fig.  24  to  be  shifted  by  about  15  Angstrom  units  toward  the  violet; 
whether  this  is  a  real  shift,  or  whether  it  is  due  to  disturbances  caused  by  simultaneous  absorp- 
tion and  luminescence  we  are  unable  to  say. 


( 

10 

1 

r 

/ 

/ 

« 

I 

/ 

/ 

A 

/ 

/ 

./ 

\l 

\ 

/ 

\ 

\ 

/ 

\ 

y 

3 

a 

1 

3 

(A. 

.48 


.50 


52/^ 


Fig.  24. — Uranyl  sulphate  (solid), 
showing  the  brightest  fluo- 
rescence band  at  about  0.51  n 
and  a  group  of  absorption 
bands  at  about  0.49  ju. 


FLUORESCENCE  AND  ABSORPTION  OF  THE  URANYL  SALTS.      37 


In  a  concentrated  solution  of  potassium  uranyl  sulphate  (see  fig.  26) 
three  absorption  bands  were  found  at  4,910,  4,730,  and  4,570.    These 


/ 

10 

h 

f 

.^^S^ 

/ 

r 

f 

1 

5 

/ 

/ 

1 

1 

; 

J 

J 

\/3 
\ 

I 
J 

/3 

^ 

/ 

r\ 

/ 

1 

5 

r^ 

1 

r 

\J 

J 

^ 

J 

/ 

\^ 

A 

6 

A 

8 

.50 

.*•  .*0  .3V  /^ 

Fig.  25. — Uranyl  sulphate  (solution),  show-  Fig.  26. — Transmission  of  a  concentrated 

ing  at  the  left  a  portion  of  the  trans-  solution  of  uranyl  potassium  sulphate, 
mission  spectrum  for  a  thin  layer  and  at 
the  right  for  a  thick  layer. 

do  not  agree  in  position  with  the  corresponding  bands  of  the  solid  salt, 
which  occur  at  4,920,  4,760,  and  4,472.  The  solution  of  the  double 
sulphate  shows  no  trace  of  fluorescence. 


IV.  PHOSPHORESCENCE  OF  THE  URANYL  SALTS. 

Concerning  the  phosphorescence  of  the  uranyl  compounds,  we  find 
little  on  record  beyond  the  early  observations  of  E.  Becquerel/  who, 
in  his  classic  paper  of  1861,  noted  the  brilhant  and  very  short-lived 
after-glow  and  made  some  observations  on  the  law  of  decay. 

For  the  study  of  the  phenomena  of  phosphorescence  in  these  sub- 
stances and  in  other  cases  having  a  duration  of  glow  of  a  few  thou- 
sandths of  a  second,  we  devised  a  new  instrument,  the  synchrono- 
phosphoroscope.  Indeed,  for  the  experiments  to  be  described  in  this 
chapter,  and  which  involved  the  use  of  surfaces  of  considerable  size, 
the  cooling  of  the  substance  during  excitation,  simultaneous  observa- 
tions during  fluorescence  and  phosphorescence,  etc.,  none  of  the  exist- 
ing forms  are  easily  adapted.  The  original  phosphoroscope  of  Bec- 
querel,^  later  modified  by  E.  Wiedemann,^  and  also  the  revolving  drum 
type  used  successively  in  various  forms  byBecquerel,*Tyndall,^Kester,^ 
and  Waggoner,^  afford  sufficient  speed,  as  does  Merritt's^  phosphoro- 
scope of  1908;  but  none  of  these  could  be  used  without  modification. 

The  new  apparatus^  consists  of  a  small  synchronous,  alternating- 
current  motor  A.  C,  figure  27,  and  a  small  direct-current  motor  D.  C. 
upon  a  common  shaft.  To  one  end  of  the  shaft  is  attached  a  sectored 
disk,  WW  J  figures  27  and  28,  with  four  equal  open  and  four  closed  sec- 
tors, corresponding  to  the  four  poles  of  the  A.  C.  motor.  On  the  cir- 
cuit of  60  cycles  this  machine,  when  brought  to  speed  by  the  D.  C. 
motor  and  released,  runs  steadily  at  30  revolutions  per  second.  A 
"step-up"  transformer  TT,  in  the  same  alternating-current  circuit, 
produces  discharges  at  the  spark-gap,  or  series  of  gaps  (^),  at  each 
alternation,  i.  e.,  120  times  a  second.  This  discharge  may  be  reduced 
to  a  single  spark  by  proper  adjustment  of  the  resistance  and  capacity 
of  the  circuit,  or  more  conveniently  for  many  purposes  the  discharge 
may  be  confined  to  the  peak  of  the  wave  by  means  of  the  four-pointed 
star-wheel  SS  (figs.  27  and  28),  which  is  mounted  on  the  shaft  and 
carefully  adjusted  as  to  phase. 

The  direct-current  motor  may  also  be  used  to  drive  the  sectored  disk 
at  other  speeds,  in  which  case  the  circuit  of  the  motor  A.  C.  is  broken 
and  the  discharge  is  derived  from  any  convenient  source  capable  of 
producing  a  proper  spark  at  each  quarter  revolution. 

^  E.  Becquerel.     Annales  de  Chimie  et  de  Physique  (3),  lxii,  p.  1.     1861. 
2  Ihid.,  Lv,  p.  5.     1859. 

•  E.  Wiedemann,  Wiedmann  a  Annalen,  xxxix,  p.  446,  1888. 

*  E.  Becquerel,  1.  c. 

^  Tyndall.     See  Lewis  Wright's  volume  on  light,  p.  152.     London,  1882. 

•  Kester,  Physical  Review  (1),  ix,  p.  164. 

'  Waggoner,  Carnegie  Inst.  Wash.  Pub.  No.  152. 

*  Nichols  and  Merritt,  Carnegie  Inst.  Wash.  Pub.  No.  152. 

"  E.  L.  Nichols:  Proc.  Nat.  Acad,  of  Scienceb,  v.  2,  p.  328.  1916.  Also  Science,  XLin, 
p.  937.     1916. 

38 


PHOSPHORESCENCE   SPECTRA. 


39 


When  the  sectored  disk  WW  is  so  adjusted  on  the  shaft  that  the 
closed  sectors  conceal  the  phosphorescent  surfac'e  during  excitation  by 
the  spark,  an  observer,  looking  through  the  open  sectors  as  they  pass, 
sees  the  phosphorescence  as  it  appears  a  few  ten  thousandths  of  a  second 
after.  The  apparatus  is  thus  suitable  for  the  study  of  phosphorescence 
of  very  short  duration  or  of  the  earliest  stages  in  cases  of  slow  decay. 
By  shifting  the  sector  on  the  shaft  it  is  possible  without  variation  in 

0 


Fig.  27. 


Fig.  28. 


the  rate  of  rotation  to  make  observations  at  the  very  beginnings  of 
phosphorescence  and  to  compare,  by  simultaneous  vision,  the  appear- 
ances just  before  and  immediately  after  the  close  of  excitation,  or, 
on  the  other  hand,  the  earlier  with  the  later  stages,  up  to  about  0.004 
second.  The  photometer,  spectroscope,  spectrophotometer,  camera, 
etc.,  may  all  readily  be  used  with  this  form  of  phosphoroscope  and 
studies  of  the  most  varied  character  become  possible. 

Phosphorescence  is  commonly  regarded  simply  as  the  after-effect  of 
fluorescence,  the  emission  spectrum  immediately  after  the  close  of  exci- 
tation being  identical  with  that  immediately  before  excitation  ceases. 
This  has  hitherto  been  only  an  assumption,  since  it  is  thinkable  that 
the  process  which  prepares  a  substance  for  phosphorescence  might  pro- 
duce emission  during  excitation  differing  from  that  which  consti- 
tutes phosphorescence  and  which  together  with  the  latter  would  be 
present  during  fluorescence.  It  is  also  thinkable,  although  unlikely, 
that  the  phosphorescence  might  contain  some  components  requiring 
a  measurable  time  for  development  and  observable  only  after  an  appre- 
ciable interval. 

This  is  a  matter  which  it  would  be  very  difficult  to  settle  in  the  cases  of 
phosphorescence  hitherto  studied,  because  the  spectrum  of  fluorescence 
and  phosphorescence  consists  of  broad  bands  or  complexes  of  overlap- 
ping bands,  and  almost  the  only  criterion  of  identity  is  that  of  color. 


40 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


The  uranyl  salts,  because  of  their  remarkable  spectra,  afford  an 
unusual  opportunity  to  establish  the  exact  relation  between  the  emis- 
sion of  light  during  excitation  and  at  various  times  after  excitation 
has  ceased,  and  it  was  for  this  purpose  that  the  first  experiments  with 
the  new  phosphoroscope  were  undertaken. 

The  method,  briefly  outlined,  is  as  follows:  The  substance,  inclosed 
in  a  flat  tube  of  glass  BA  about  8  cm.  long  and  2  cm.  wide,  is  viewed 
through  the  rapidly  revolving  sectored  disk  of  the  synchrono-phos- 
phoroscope.  It  is  mounted  vertically,  with  its  axis  at  right  angles  to 
the  radius  of  the  disk,  as  shown  in  figure  29. 


Fig.  29. 


Fig.  30. 


It  is  uniformly  excited  by  zinc  sparks  120  times  a  second  while 
hidden  by  the  closed  sectors  and  is  visible  for  1/240  of  a  second  during 
the  passage  of  each  of  the  intervening  open  sectors. 

A  phosphorescent  substance  of  slow  decay  appears  under  these  cir- 
cumstances to  be  equally  bright  from  top  to  bottom,  but  if  one  of  the 
uranyl  salts,  such  as  the  double  uranyl-ammonio  sulphate,  which  was 
the  substance  selected  for  detailed  study,  be  used,  it  appears  a  very 
bright  green  at  the  bottom  of  the  tube,  shading  off  to  bare  visibility 
at  the  top. 

The  rate  of  decay  of  this  substance  and  of  the  other  uranyl  salts 
is  so  rapid  that  the  upper  end  of  the  tube,  which  is  seen  at  the  intensity 
which  corresponds  approximately  to  the  instant  0.003  second  after 
excitation,  has  only  a  small  fraction  of  the  brightness  of  the  lower  end, 
which  is  viewed  about  0.0005  second  after  excitation. 

The  particular  salt  mentioned  above  was  selected  because  at  low 
temperatures  its  spectrum  is  unusually  well  resolved  in  groups  of  com- 
plexes of  narrow,  line-like  bands,  making  it  possible  to  detect  changes  in 
the  individual  components. 

To  obtain  simultaneous  observations  a  pair  of  right-angled  prisms 
was  mounted  before  the  sht  of  a  Hilger  spectroscope,  as  shown  in 
figure  30. 

Light  from  the  lower  end  of  the  tube  A  enters  the  lower  half  of  the 
slit.  That  from  the  upper  end  By  after  two  total  reflections,  enters 
the  upper  half  of  the  slit,  and  we  have  two  spectra  one  above  the  other, 


PHOSPHOEESCENCE    SPECTRA. 


41 


FiQ.  31o. 


FiQ.  316. 


coinciding  throughout  as  to  wave-length,  but  separated  by  a  dark  Une 
formed  by  the  lower  edge  of  the  second  prism  {R'), 

To  compare  fluorescence  with  phosphorescence,  the  sectored  disk  was 
shifted  upon  its  shaft  until  the  lower  end  of  the  tube  was  viewed  during 
excitation,  the  upper  end  immediately  after  (fig.  31a).  To  compare 
the  phosphorescence  spectrum  at  an  earlier  and  later  stage,  the  disk 
was  so  set  that  its  position  at  the  moment  of  excitation  was  as  shown 
in  figure  316.  By  means  of  the  reflecting  prisms  at  the  sUt  of  the  spec- 
troscope, already  described,  the  spectrum  of  the  light  emitted  from 
region  A  was  compared  with 
that  at  B  in  each  case.  At 
-f-20°  C.  the  banded  spectra 
were  found  to  be  identical 
in  every  respect,  except  in 
brightness ;  and  the  same  was 
true  at  low  temperatures, 
where  it  was  possible  to  in- 
spect each  of  the  numerous 
line-like  bands  individually. 

Of  the  seven  homologous  series  distinguishable  in  the  fluorescence 
spectrum,  all  were  present  in  phosphorescent  light,  unshif  ted  as  to  posi- 
tion and  not  perceptibly  enhanced  or  diminished  in  relative  brightness. 

The  comparison  was  less  satisfactory  as  regards  minor  details  in  the 
case  of  the  early  and  late  stages  of  phosphorescence,  some  of  the  fainter 
bands  being  invisible,  but  changes  such  as  might  be  looked  for,  ^.  e., 
those  due  to  the  greater  persistence  of  certain  series,  could  scarcely 
have  escaped  notice. 

The  significance  of  these  observations  is  two-fold :  On  the  one  hand 
we  find  that  for  the  only  examples  of  luminescence  which  admit  of  such 
detailed  inspection  the  spectrum  of  phosphorescence  is  identical  with  that 
of  fluorescence,  and  since  there  are  no  indications  to  the  contrary  in  the 
case  of  other  classes  of  substances  thus  far  studied,  it  is  probable  that 
the  above  statement  will  apply  to  all  phosphorescent  materials.  On 
the  other  hand,  we  find  that,  in  spite  of  its  great  complexity,  the  lumi- 
nescence spectrum  of  a  uranyl  salt  is  to  be  regarded  as  a  unit,  all  its 
components  decaying  at  the  same  rate  after  the  cessation  of  excitation. 

Thus  this  class  of  substances  (i.  e.,  the  uranyl  salts)  not  only  conform 
to  the  first  three  criteria  of  homogeneity  discussed  in  Chapter  II  but 
likewise  to  that  based  upon  the  phenomena  of  phosphorescence. 

CURVES  OF  DECAY. 

To  determine  the  change  of  intensity  of  phosphorescence  with  the 
time  a  simple  form  of  photometer  previously  used  in  a  study  of  the 
phosphorescence  of  kunzite^  was  mounted  in  front  of  the  sectored  disk. 


^  Nichols  and  Howes,  Physical  Review  (2),  iv,  p.  19.     1914. 


42 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


A  lateral  strip  of  the  phosphorescent  salt  1  cm.  wide  was  excited  by 
sparks  from  a  single  spark-gap  between  zinc  terminals  and  measure- 
ments of  the  brightness  were  made  at  various  times  after  the  close  of 
excitation.  The  necessary  conditions  were  attained  by  shifting  the 
disk  successively  through  small  angles,  so  as  to  vary  the  interval 
between  excitation  and  observation.  The  time  could  be  estimated 
with  sufficient  accuracy  by  noting  the  instantaneous  positions  of  the 
disk  for  each  adjustment,  as  given  by  the  strictly  synchronous  illumina- 
tion due  to  the  spark. 


I 

1 


X 


zx^ 

Y 

— >— - 

L 

N 

s 

-0 


L.l. 


Fig.  32. 

The  arrangement  of  the  apparatus  is  shown  in  figure  32,  in  which  P 
is  the  phosphorescent  surface,  DD  the  sectored  disk,  L.  B.  the  Lummer- 
Brodhun  cube  of  the  photometer,  E  the  eyepiece,  S  a  color-screen  and 
matte  translucent  plate,  C  the  comparison  lamp  which  traveled  along 
the  track  of  an  optical  bench.  The  cross  at  Z  indicates  the  position 
of  the  spark-gap. 

In  table  15  relative  intensities  /,  the  reciprocals  l/A/i7and  times  T 
after  excitation  are  given.  Figure  33  shows  the  relations  between  / 
and  r,  and  l/VFand  T  respectively  in  the  usual  manner. 

Table  15. 


T. 

/. 

1/V/. 

T. 

/. 

i/vr 

0.000479 

59.49 

0.130 

0.00170 

2.03 

0.702 

.000637 

27.78 

.190 

.00193 

.971 

1.014 

.000856 

16.02 

.250 

.00212 

.610 

1.280 

.000949 

12.62 

.281 

.00247 

.296 

1.836 

.00110 

9.80 

.319 

.00287 

.159 

2.624 

.00146 

6.03 

.446 

As  appears  from  the  table  and  curve  ABC,  figure  33,  this  substance 
exhibits  a  remarkably  rapid  decay,  falling  in  the  interval  between 
0.0005  second  after  close  of  excitation  and  0.003  second  to  less  than 
three-thousandths  of  its  intensity  at  the  beginning  of  that  interval. 
To  show  the  degree  of  accuracy  with  which  the  lower  intensities  were 
observed,  the  portion  of  the  curve  BC  is  reproduced  with  ordinates 
magnified  ten  times  B'C.  _The  results  are  Hkewise  plotted  in  the  cus- 
tomary manner  with  1/V/  as  ordinates  (curve  DEF),  and  this  brings 


PHOSPHORESCENCE    SPECTRA. 


43 


out  an  unusual  characteristic.  It  is  usual  to  find  two  processes  o 
phosphorescence  succeeding  one  another  and  represented  by  the  two 
straight  arms  of  the  curve  DE  and  FGj  but  in  all  the  numerous  cases 
hitherto  described,  excepting  two  to  be  discussed  in  a  subsequent  para- 
graph, the  later  process  (FG)  is  indicated  by  a  curve  of  lesser  slope. 
In  the  case  of  this  uranyl  salt,  however,  FG  trends  very  sharply  up- 
ward, showing  a  greatly  accelerated  decay. 


t.  URANYL  AMMONIUM  SULPHATE. 

2.URANYL  POTASSIUM    SULPHATE. 

3. URANYL   NITRATE. 

4. URANYL   SULPHATE. 

5. URANYL  AMMONIUM  CHLORIDE. 


0.0 


.001 


.003  SEC, 


Fig.  33. 


Fig.  34. 


By  means  of  these  preliminary  observations  certain  facts  may  be 
regarded  as  established.^    These  may  be  sununarized  as  follows: 

(1)  There  is  no  appreciable  change  of  color  during  decay. 

(2)  The  decay  of  phosphorescence  is  exceedingly  rapid,  the  intensity 
falling  to  one-thousandth  of  its  initial  value  within  0.0035  second. 

(3)  The  very  complex  fluorescence  spectrum  at  — 180°  C.  is  identical 
in  structure  and  relative  distribution  of  intensities  with  that  observed 
during  the  earlier  and  later  stages  of  phosphorescence. 

^  Nichols,  Proceedings  National  Academy  of  Sciences,  vol.  ii,  p.  328.     1916. 


44 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  16. 


(4)  The  curve  of  decay  of  phosphorescence  differs  from  the  prevailing 
type  in  that  although  as  usual  two  successive  processes  are  distinguish- 
able, the  second  process  is  more  rapid  instead  of  being  slower  than  the 
first. 

The  study  of  these  phenomena  has  since  been  extended  to  several 
other  typical  uranyl  salts,  the  curves  of  decay  of  which  were  deter- 
mined by  the  method  just  described  and  under  conditions  of  excita- 
tion, etc.,  as  nearly  constant  as  possible.^  These  curves  of  decay  are 
of  the  same  new  type  originally  found  in  the  uranyl  ammonium  sul- 
phate. The  two  processes,  as  determined  by  the  customary  method  of 
plotting  / -1/2  as  a  function  of  the  time  are  indicated  by  straight  lines 
differing  from  one  another  in  slope  and  the  second  process  has  in  all 
cases  the  steeper  gradient.  Later  experiments,  in  which  the  intensity 
of  excitation  was  increased,  revealed  the  presence  of  a  third  process  not 
included  within  the  interval  of  time  covered  by  our  earher  experiments. 

STUDIES  INVOLVING  THE  FIRST  AND  SECOND  PROCESSES. 

The  curves  shown  in  figures  34  and  35  are  typical  of  the  results 
obtained  with  all  the  salts  under  observation.  They  represent  the 
decay  of  the  phosphorescence  of  the  compounds  shown  in  table  16. 

The  initial  intensity,  under  like 
excitation,  varies  greatly  in  the 
different  salts,  as  also,  to  some  ex- 
tent, does  the  rate  of  decay.  It  will 
be  noted  that  the  initial  intensities 
of  the  anamonium  and  potassium 
sulphates,  for  example,  are  several 
times  greater  than  those  of  the 
nitrate,  the  sulphate,  and  the  am- 
monium chloride.  This  is,  however,  a  question  of  previous  history  as 
well  as  of  chemical  and  physical  constitution,  as  was  determined  in 
the  following  manner: 

Uranyl  potassium  sulphate  was  dissolved  in  hot  water  and  a  mass  of 
the  minute  crystals  which  were  thrown  down  on  cooling  the  solution 
were  immediately  sealed  up  in  a  glass  tube.  Care  was  taken  through- 
out these  manipulations  to  protect  the  precipitate  from  the  action  of 
fight. 

This  sample,  still  in  darkness,  was  mounted  in  the  synchrono-phos- 
phoroscope  and  a  curve  of  decay  was  taken,  the  first  exposure  to  excit- 
ing light  being  that  at  the  beginning  of  the  run.  The  substance  then 
showed,  temporarily,  a  brilliancy  of  phosphorescence  much  above  that 
to  be  obtained  under  ordinary  circumstances,  but  was  soon  reduced  to 
its  normal  and  semi-permanent  condition,  after  which  the  usual  curve 
of  decay  was  obtained. 

^  Nichols  and  Howes,  Physical  Review  (2),  ix,  p.  292.     1917. 


Curve. 

Substance. 

1 
2 
3 
4 
5 

Uranyl  ammonitim  sulphate. 
Uranyl  potassium  sulphate. 
Uranyl  nitrate  +  6H2O. 
Uranyl  sulphate. 
Uranyl  ammonium  chloride. 

PHOSPHORESCENCE   SPECTRA. 
EXCITATION  IN  THE  PRESENCE  OF  RED  AND  INFRA-RED  RAYS. 


45 


To  determine  whether  red  or  infra-red  rays  have  an  effect  on  these 
substances  similar  to  that  observed  in  the  case  of  the  phosphorescent 
sulphides,  a  modification  of  the  apparatus  was  made  such  that  the 
surface  under  examination  could  be  subjected  to  the  intense  illumina- 
tion obtained  by  focusing  the  crater  of  an  electric  arc  upon  it.  A  screen 
of  excellent  ruby  glass  was  interposed  to  cut  off  all  but  the  longer  waves 
and  observations  were  made  through  a  screen  quite  impervious  to  red. 

Exposure  to  this  source  was  found  to  affect  measurably  neither  the 
brightness  of  fluorescence  nor  of  phosphorescence.  Curves  taken  after 
exposure  to  this  source,  those  taken  with  the  substance  subjected  to 
it  interruptedly  throughout  the  run,  and  curves  in  the  determination 
of  which  readings  were  taken  alternately  with  and  without  red  Ught 
were  all  identical  with  those  taken  in  entire  absence  from  such  expos- 
ures. The  striking  contrast 
between  this  negative  result 
and  the  well-known  effects  of 
infra-red  radiation  upon  the 
phosphorescence  of  the  sul- 
phides is  notable. 

The  observations  already 
cited,  showing  the  complete 
identity  of  the  spectrum  of 
fluorescence  with  that  of  phos- 
phorescence seemed  to  indicate 
that  the  intensity  would  go 
over  from  that  of  fluorescence 
to  that  of  phosphorescence 
without  discontinuity.  This 
conclusion  was  confirmed, 
within  the  errors  of  observa- 
tion, by  measurements  just 
before  and  after  the  close  of 
excitation.  The  only  previous 
instances  where  this  relation 
has  been  experimentally  established,  so  far  as  we  know,  are  to  be  found 
in  Waggoner's^  studies  of  phosphorescence  of  short  duration  and  in 
recent  observations  on  the  luminescence  of  kunzite.^ 

In  view  of  the  unexpected  character  of  the  decay  curves  for  the  phos- 
phorescence of  the  uranyl  compounds,  the  question  arises  whether  the 
rather  unusual  mode  of  excitation  employed,  i.  e.,  periodically  repeated 
exposures,  120  times  a  second,  to  groups  of  sparks  of  high  frequency, 
might  produce  such  a  result,  or  whether  the  decay  curves  are  character- 

^  Waggoner,  Physical  Review,  xxvii,  p.  209. 

'  Nichols  and  Howes,  Physical  Review  (2),  iv,  p.  26. 


i-r 

s. 

80 

4. 

/ 

/ 

/ 

1.    to 

60 

// 

/ 

/ 

/-- 

40 

// 

/ 

/ 

40 

20 

A 

^ 

/ 

•to 

//. 

% 

.001 

.002 

SEC. 

^ 

1 

1 

Fig.  35. 


46 


FLUORESCENCE    OF  THE   URANYL   SALTS. 


istic  of  this  class  of  compounds,  whatever  the  mode  of  excitation.  It 
is  true  that  both  Waggoner^  and  Zeller,^  using  a  Merritt  phosphoro- 
scope,  found  in  their  studies  of  phosphorescence  of  short  duration  that 
excitation  by  means  of  a  spark  discharge  very  similar  to  our  own  gave 
decay  curves  of  the  usual  type. 

It  is  also  obvious  from  the  measurements  already  described  that  the 
interval  between  excitation,  i.  e.,  1/120  second,  is  sufficient  for  the  com- 
plete discharge  of  the  phosphorescent  glow,  and  since  the  absence  of 
any  effect  of  red  and  infra-red  indicates  that  there  is  no  storage  of 
undeveloped  energy  to  be  carried  over,  such  as  occurs  in  the  phosphor- 
escent sulphides,  it  seems  probable  that  the  decay  curves  do  not  vary 
greatly  from  that  which  might  be  obtained,  were  it  possible  to  make  the 
experiment,  from  a  single  exposure. 

To  test  this  a  run  was  made  upon  the  sample  of  uranyl  ammonium 
sulphate  previously  used,  but  with  the  Merritt  phosphor oscope. 

By  driving  the  disk  of  this  instrument  3,000  revolutions  a  minute, 
much  the  same  range  of  time  intervals  was  available  as  with  the 
synchrono-phosphoroscope. 

To  further  vary  the  conditions,  a  quartz  mercury  arc  was  substituted 
for  the  spark-gap  of  Waggoner  and  Zeller.  The  arrangement  of  appar- 
atus was  as  shown  in  figure  36, 
in  which  DD  is  the  revolving 
disk,  H  the  mercury  lamp,  P  the 
phosphorescent  substance,  LB  s.&e 
the  Lummer-Brodhun  cube  of 
the  photometer,  SS  a  color- 
filter  and  milk-glass  screen.  The 
device  for  shifting  the  oblique 
mirror  M  with  reference  to  the 
aperture  A  in  the  disk  is  not 
shown. 

Although  the  decay  was  some- 
what more  rapid  in  this  determination  on  account  of  the  less  intense 
excitation,  the  curve  was  of  precisely  the  type  obtained  by  the  prev- 
ious method. 

Measurements  upon  some  of  the  bands  of  brief  duration  in  the  spec- 
trum of  the  phosphorescent  sulphides,  recently  made  with  the  syn- 
chrono-phosphoroscope under  experimental  conditions  identical  with 
those  here  described,^  yield  curves  of  the  usual  type  associated  with 
these  sulphides,  so  that  the  question  of  the  change  of  form  being  due 
to  the  phosphoroscope  employed  is  effectually  eliminated. 


/ 


L.B. 


o 


Fig.  36. 


1  Waggoner,  Physical  Review,  xxvii,  p.  209. 

2  Zeller,  Physical  Review,  xxxi,  p.  367. 

3  Nichols,  Proc.  Am.  Philosophical  Society,  lv,  p.  494.     1916. 


PHOSPHORESCENCE   SPECTRA. 


47 


SOLID  SOLUTIONS  AND  SEMI-FLUIDS. 
The  uranyl  salts  differ  from  nearly  all  if  not  all  phosphorescent  sub- 
stances hitherto  studied.  We  do  not  have,  as  in  the  phosphorescent 
sulphides,  the  preparations  of  Waggoner,  the  ruby,  etc.,  to  deal  with  a 
trace  of  active  material  in  solid  solution,  but  with  compounds  that  are 
in  themselves  brilliantly  phosphorescent.  If  the  peculiar  character  of 
the  curve  of  decay  is  due  to  that  fact  it  might  be  expected  that  uranium 


Fig.  37 


Fig.  38. 


glass,  in  which  the  active  material  is  considered  to  be  in  a  state  of  solid 
solution,  would  have  a  law  of  decay  corresponding  to  the  prevailing 
type  for  such  solutions,  i.  e.,  with  the  first  process  as  indicated  by  the 
curve  for  /-1/2,  and  time,  represented  by  a  line  of  steeper  slope  than  the 
line  for  the  second  process.  A  piece  of  uranium  glass  gave,  however, 
a  decay  curve  similar  to  those  of  the  uranyl  salts  (see  fig.  37) .    Another 


48 


FLUORESCENCE    OF   THE   URANYL    SALTS. 


preparation  which  differs  from  most  of  the  uranyl  salts  is  the  uranyl 
sodium  phosphate,  a  sample  of  which  was  made  by  D.  T.  Wilber  for 
certain  studies  in  fluorescence  recently  published.^  This  substance  is 
a  very  viscous  liquid  with  the  characteristic  green  fluorescence  of  the 
uranyl  compounds. 

One  might  expect,  in  accordance  with  the  findings  of  Becquerel  for 
liquids  in  general,^  that  there  would  be  no  observable  after-glow.    It 


EFFECT   OF  TEMPERATURE 
ON 

60  ' 

URANYL  AMMONIUM  NITRATE 
I  '2 

/ 

20* 

50 

/ 

/ 

i®                                                                  / 

/• 

19                                    1 

/ 

-180* 

20                                                   k 

/ 

/ 

JO                                   // 

^ 

/ 

.00.                ,                ^               , 

r 

1 

jopr  SEC. 

Fig.  39. 

is  true  that  Becquerel  expressed  the  belief  that  with  a  phosphoroscope 
of  sufficient  speed,  phosphorescence  would  probably  be  detected  in 
fluorescent  liquids,  but  no  one,  so  far  as  we  know,  save  Dewar  in  an 
unconfirmed  statement  concerning  a  supposed  phosphorescence  of 
liquid  air,  has  since  that  time  (1859)  recorded  an  instance  of  phos- 
phorescence excepting  in  solids  and  gases. 

When  a  tube  containing  the  phosphate  was  tested  with  the  syn- 
chrono-phosphoroscope  no  phosphorescence  was  found  of  duration 

1  Howes  and  Wilber,  Physical  Review  (2),  vol.  7,  p.  394.     Mar.  1916. 

2  See  E.  Becquerel,  La  Lumiere,  vol.  i,  chapter  on  Phosphorescence. 


PHOSPHORESCENCE   SPECTRA. 


49 


sufficient  to  be  detected.  Another  sample  so  prepared  as  to  reduce  the 
amount  of  water  to  a  minimum  did,  however,  exhibit  phosphorescence 
of  measurable  duration.  This  preparation,  so  slow  was  its  rate  of 
flow,  might  be  regarded  as  a  plastic  solid  rather  than  a  viscous  liquid. 
A  bead  of  microcosmic  salt,  colored  in  the  usual  manner  with  uranium 
oxide,  was  comparable  in  its  phosphorescence  with  canary  glass. 


Fig.  40. 

It  appears  that  the  persistence  of  luminescence  is  due  to  the  con- 
sistency of  the  substance  and  disappears  as  the  fluidity  increases;  also 
that  the  peculiar  type  of  decay  here  described  is  common,  not  only  to 
the  crystalline  uranyl  salts  in  general,  but  also  to  the  gelatinous  forms, 
as  in  this  double  salt,  and  to  substances  in  which  uranium  appears  in 
solid  solution,  as  in  the  case  of  the  canary  glass. 

THE  THIRD  PROCESS. 

E.  Becquerel,^  in  the  course  of  his  great  pioneer  work  on  phosphores- 
cence, made  a  number  of  observations  on  the  uranyl  salts  and  on 

1 E.  Becquerel,  Annales  de  Chimie  et  de  Physique  (3),  lxii,  p.  1.     1861. 


50  FLUORESCENCE    OF   THE   URANYL   SALTS. 

uranium  glass.  He  noted  the  brilliant  initial  intensity  and  very  rapid 
decay,  and  to  test  the  independence  of  the  constant  in  his  equation  of 
decay  when  the  illumination  varied  he  made  many  measurements.  If 
from  his  data  we  compute  / -1/2,  as  a  function  of  the  time,  we  obtain 
curves  of  the  same  general  form  as  those  in  figure  32. 

BecquereFs  observations  are  not  numerous  enough,  taken  by  them- 
selves, to  determine  completely  the  type  of  curve.  His  measurements, 
however,  cover  a  larger  time  interval  than  ours  and  the  values  for  the 
longest  times  indicate  an  even  more  rapid  decay  following  the  second 
process.  We  had,  indeed,  found  some  indications  of  a  similar  tendency 
which  had  been  omitted  from  our  curves  as  lying  almost  beyond  the 
range  of  definite  determination. 

To  investigate  the  further  trend  of  the  curves  of  decay,  the  intensity 
of  excitation  was  increased  by  readustment  of  the  sparking  circuit,  by 
which  means  it  was  found  possible  to  extend  the  time  interval  for  more 
than  0.006  second  beyond  the  cessation  of  excitation. 

Careful,  often  repeated  measurements,  of  the  various  salts  showed 
in  fact  a  third  linear  process  beginning  where  our  previous  determina- 
tions had  ceased  and  having  a  steeper  slope,  indicative  of  still  more 
rapid  decay.    Typical  results  are  indicated  in  figures  38,  39,  40,  etc. 

These  processes  may  be  numbered  for  convenience  1,  2,  and  3  in  the 
order  in  which  they  occur.  Processes  1  and  2  are  in  general  of  about 
equal  duration  for  a  given  salt.  The  abruptness  of  transition,  however, 
varies  greatly,  and  in  some  instances  the  change  of  slope  is  so  gradual 
as  to  encroach  seriously  on  process  2  at  both  ends. 

THE  INFLUENCE  OF  TEMPERATURE. 

The  only  previous  instances  of  decay  of  phosphorescence  in  which  the 
later  stages  are  more  rapid  than  those  preceding  are  noted  by  Ives  and 
Luckiesh^  in  their  study  of  the  influence  of  temperature  on  phosphores- 
cence, and  by  E.  H.  Kennard^  in  a  more  recent  paper. 

Ives  and  Luckiesh  measured  the  phosphorescence  of  one  of  Lenard 
and  Klatt's  sulphides  (BaBiK  from  Leppin  and  Masche).  This  sub- 
stance was  found  to  be  very  sensitive  to  change  of  temperature  and 
the  results  at  0°,  22°,  and  35°,  C.  when  plotted  for  7-1/2  and  time  in  the 
usual  manner,  gave  curves  varying  greatly  in  slope.  The  curve  for  0° 
is  concave  toward  the  time  axis,  that  for  22°  linear,  and  that  for  35° 
strongly  convex.  They  show  that  a  linear  relation  may  be  obtained  for 
each  of  these  curves  by  varying  the  exponent  of  7. 

The  effect  of  temperature  in  the  case  of  the  phosphorescent  sul- 
phides, where  one  has  to  do  with  a  composite  of  many  overlapping 
bands  of  varying  duration,  is  undoubtedly  different  from  that  to  be 

*  Ives  and  Luckiesh,  Astrophysical  Journal,  xxxvi,  p.  330  (1912). 
*Kennard,  Physical  Review  (2),  iv,  p.  278  (1914). 


PHOSPHORESCENCE   SPECTRA. 


51 


expected  with  the  uranyl  salts,  where  the  spectrum,  in  spite  of  its 
complexity  of  structure,  is  a  unit.  It  was  deemed  of  interest,  however, 
to  determine  the  effect  of  temperature  upon  the  latter. 

For  this  purpose  a  specimen  of  the  uranyl  ammonium  nitrate  was 
mounted  within  a  cylindrical  Dewar  flask  with  unsilvered  walls  and  its 
decay  of  phosphorescence  was  determined  with  a  synchrcno-phos- 
phoroscope  at  a  temperature  a  few  degrees  above  that  of  liquid  air 
(about  —180°)  at  +20°  and  at  +60°.  The  last-named  temperature 
was  maintained  during  the  run  by  means  of  an  electrical  heating-coil. 


Fig.  41. 


The  principal  change  consists  in  a  marked  retardation  of  decay  with 
lowering  temperature  (see  fig.  39),  but  this  is  not  a  universal  charac- 
teristic of  the  uranyl  compounds.  Uranyl  ammonium  sulphate,  for 
example  (fig.  40),  is  but  slightly  influenced  in  its  rate  of  decay  by 
change  of  temperature  and  the  curve  for  - 180°  is  intermediate  between 
those  for  +20°  and  +60°. 


52 


FLUORESCENCE   OF  THE   URANYL   SALTS, 


THE  EFFECT  OF  VARYING  THE  INTENSITY  OF  EXCITATION. 

To  determine  the  effect  of  the  intensity  of  excitation,  a  series  of 
measurements  were  made  with  the  spark-gap  at  various  distances  from 
the  phosphorescent  surface.  The  substance  observed  in  these  experi- 
ments was  uranyl  rubidium  nitrate.  It  was  found  possible  to  make 
observations  of  the  decay  of  phosphorescence  with  the  excitation 
reduced  to  a  two-hundredth  of  that  usually  employed. 

From  the  curves  obtained,  of  which  four  are  given  in  figure  41,  it 
will  be  noted  that  all  three  processes  are  present,  whatever  be  the 
intensity  of  the  exciting  light;  also  that,  taken  roughly,  processes  1 
and  2  are  of  nearly  equal  duration,  and  that  with  decreasing  intensity 
of  excitation  the  duration  of  each  of  these  processes  diminishes. 


DURATION      OF    PROCESSES 

WITH  EXCITATION 

1. 

1. 

/ 

ICi2. 

M 

/ 

JO 

•                                              / 

\ 

^x 

/ 

.» 

•/ 

/ 

Y 

i^ 

M 

y 

/ 

M 

d 
2 

.002 

Fig!  42. 


.003 


SEC. 


These  relations  are  better  shown  in  figure  42,  in  which  the  duration 
of  process  1  and  the  sum  of  the  duration  of  processes  1  and  2,  counting 
from  the  close  of  excitation,  are  plotted,  with  the  intensity  of  the  ex- 
citing light  as  ordinates.  Approximately  in  both  cases  the  duration  is 
proportional  to  the  natural  logarithm  of  the  excitation.    (See  table  17.) 

This  decrease. in  the  duration  of  the  two  processes  with  falling 
excitation  affords  an  obvious  explanation  of  the  varying  character  of 


PHOSPHORESCENCE   SPECTRA. 


53 


the  curves  of  decay  of  phosphorescent  substances.  Where  the  excita- 
tion is  chiefly  superficial,  as  in  the  case  of  some  powders,  the  excitation 
may  be  nearly  of  one  intensity  and  the  curve  made  up  of  well-defined 
Hnear  processes  with  sharp  inflection-points.  We  have  found  this  to 
be  the  case  in  many  instances.  Where,  on  the  other  hand,  fluorescence 
is  excited  within  the  crystalline  mass  by  rays  that  have  suffered  con- 
siderable loss  by  absorption,  etc.,  there  will  be  a  wide  range  of  intensi- 
ties of  excitation  and  a  curve  results  with  distributed  knees  and  linear 
processes  shortened  and  sometimes  almost  obliterated.  We  observed 
this  particularly  where  a  clear  crystal  was  mounted  with  faces  per- 
pendicular to  the  photometer  and  was  excited  from  behind  so  that  the 
light  emitted  by  the  surface  nearest  the  exciting  source  passed  through 

Table  17. — Variation  of  length  of  processes  with  excitation  {phosphorescence  of  uranyl 

rubidium  nitrate). 


Intensity  of 

excitation 

{E). 

Nat.  log. 
E. 

Duration. 

Process 
1. 

Process 
2. 

Process 
1+2. 

sec. 

sec. 

sec. 

41.70 

6.033 

0.0022 

0.0018 

0.00400 

13.70 

4.919 

.00170 

.0014 

.00310 

2.52 

3.220 

.00147 

.000993 

.00240 

1.35 

2.590 

.00118 

.00080 

.00198 

.900 

2.190 

.00080 

.00090 

.00170 

.476 

1.560 

.00070 

.00076 

.00146 

.201 

.698 

.00050 

.00060 

.00110 

the  crystal  and  was  partially  absorbed.  Excitation  occurred  within 
the  crystal  in  diminishing  amount  with  increasing  depth  and  the  com- 
posite phosphorescence  reaching  the  eye  under  such  conditions  showed 
this  blending  effect  to  a  marked  degree.  The  same  crystal  when 
excited  from  in  front  gave  a  curve  in  which  the  angles  between  pro- 
cesses were  made  more  sharply  defined.  The  effect  in  question  is 
probably  a  general  one  and  may  well  account  for  the  perplexing  differ- 
ences in  the  curves  of  decay  obtained  under  shghtly  varying  circum- 
stances. Thus,  one  observer  will  obtain  an  angular  curve,  where 
another,  studying  the  same  material,  can  detect  no  linear  processes. 
The  same  observer,  indeed,  in  attempting  to  repeat  his  measurements, 
will  often  find  the  above-mentioned  change  of  type  under  conditions 
which  seem  to  be  identical  but  in  which  the  same  relations  as  regards 
superficial  and  internal  excitation  are  not  preserved. 

We  found  in  the  study  of  this  effect  a  crystal  one  smooth  face  of  which 
gave  the  blended  curve,  while  the  opposite  face,  which  was  rough,  gave 
the  angular  curve,  a  change  produced  and  reproducible  by  merely 
rotating  the  crystal  through  180°. 


54 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


THE  PHOSPHORESCENCE   OF  VARIOUS  NITRATES. 

Observations  were  made  on  a  series  of  nitrates  previously  prepared 
for  the  detailed  comparison  of  the  fluorescence  spectra  of  that  salt.^ 
These  consist  of  crystals  with  6  H2O  (rhombic),  3  H2O  (triclinic),  and 
2  H2O  (system  undetermined)  as  water  of  crystallization  and  a  speci- 
men sealed  in  glass  which  had  been  rendered  as  nearly  anhydrous  as 
was  possible  without  decomposing  the  nitrate. 

The  curves  of  decay  indicate  a  much  slower  rate  of  decay  for  the 
crystalline  forms  than  for  the  anhydrous  nitrate.  Whatever  effect  the 
amount  of  water  of  crystallization  may  have  is  doubtless  masked  by  the 
far  greater  influence  of  the  crystalline  form.  This  is  perhaps  to  be 
expected,  since,  as  will  be  shown  in  Chapter  VII,  these  specimens  exhibit 
as  great  differences  in  the  structure  and  appearance  of  their  fluores- 
cence and  absorption  spectra  as  commonly  exist  between  entirely 
distinct  uranyl  salts.  Similar  differences  in  the  case  of  salts  similar  in 
composition  but  differing  in  crystalUne  form  will  likewise  be  described 
in  a  subsequent  chapter. 


Fig.  43. 
OBSERVATIONS  ON  POLARIZED  PHOSPHORESCENCE. 

Certain  crystals  of  the  double  chlorides  of  uranyl  exhibit  fluorescence 
spectra  consisting  of  sets  of  bands  polarized  at  right  angles  to  one 
another.  To  determine  whether  these  components  after  the  close  of 
excitation  decay  independently  or  without  change  in  their  relative 
intensities,  the  following  experiment  was  made : 

A  crystal  of  the  rubidium  uranyl  chloride  that  exhibited  the  phe- 
nomenon of  polarized  fluorescence  was  mounted  behind  the  disk  of  the 
synchrono-phosphoroscope  and    was  observed  with  a  spectroscope. 

^Nichols  and  Howes;  Physical  Review  (2),  ix,  p.  292.     1917. 


PHOSPHORESCENCE   SPECTRA.  55 

The  slit  of  the  latter  instrument  was  divided  into  two  parts  by  means 
of  an  opaque  strip  across  the  middle  {S,  fig.  43). 

Within  the  collimator  a  doubly  refracting  rhomb  R  and  Nicol 
prism  N  were  mounted.  The  rhomb  gave  two  slit-images  vertically 
displaced  and  the  adjustment  was  such  that  the  lower  part  (A)  of  one 
image  was  contiguous  with  the  upper  part  (B)  of  the  other. 

Thus  two  spectra  of  the  phosphorescent  field  were  obtained  corre- 
sponding to  the  two  polarized  components.  These  presented  the  usual 
distinctive  structures  at  whatever  stage  of  the  phosphorescent  decay 
they  were  observed.  By  rotation  of  the  Nicol  prism  the  two  fields 
could  be  brought  to  equal  brightness  for  any  given  part  of  the  spec- 
trum, and  this  balance,  if  made  with  the  sector  of  the  phosphoroscope 
set  so  as  to  give  observations  at  0.0005  second  after  extinction,  was 
found  equally  correct  up  to  0.005  second  or  as  long  as  phosphorescence 
was  observable.  The  two  components  therefore  decay  at  the  same 
rate. 

SUMMARY  OF  PHOSPHORESCENCE  OF  SHORT  DURATION. 

(1)  All  uranyl  salts  thus  far  examined  possess  the  same  type  of 
phosphorescence;  i.  e.,  with  increasing  instead  of  diminishing  rates  of 
decay. 

(2)  This  is  true  not  only  of  the  crystalline  forms,  but  also  of  uranyl 
compounds  in  solid  solution  or  in  the  plastic  state  characteristic  of  the 
double  phosphates. 

(3)  The  initial  brightness  of  phosphorescence  under  like  excitation 
varies  greatly  with  the  different  salts,  as  does  also  to  some  extent  the 
rate  of  decay. 

(4)  The  brightness  of  a  salt  newly  prepared  in  darkness  is  greater 
when  first  excited  than  subsequently,  but  it  soon  reaches  a  nearly 
stable  condition. 

(5)  Exposure  to  red  and  infra-red  rays  is  without  effect  as  regards 
the  rate  of  decay. 

(6)  The  phosphorescence,  like  the  fluorescence,  of  the  uranyl  salts 
appears  to  be  independent  of  the  mode  of  excitation,  and  the  structure 
of  the  intricate  spectrum  is  the  same  during  excitation  and  throughout 
the  observable  phosphorescent  interval. 

(7)  Changes  in  the  rate  of  decay  are  not  continuous,  but  occur  in 
definite  steps,  there  being  at  least  three  successive  processes  within  the 
interval  covered  by  observations,  ^.  e.,  about  0.006  second.  These 
processes  follow  a  law  such  that  /-1/2  is  in  linear  relation  to  the  time. 

(8)  The  first  and  second  processes,  counting  from  the  close  of 
excitation,  are  of  nearly  equal  duration,  increasing  in  duration  with 
the  intensity  of  excitation  in  such  a  manner  that  the  duration  of  the 
process  is  approximately  proportional  to  the  natural  logarithm  of  the 
excitation. 


56  FLUORESCENCE   OF  THE   URANYL   SALTS. 

(9)  In  certain  salts,  such  as  uranyl  ammonium  nitrate,  decay  is 
retarded  by  cooling;  in  other  cases  the  temperature  effect  is  slight. 

(10)  Uranyl  nitrates  with  2,  3,  and  6  molecules  of  water  of  crystal- 
lization vary  greatly  in  the  rate  of  decay,  but  the  changes  in  crystalline 
form  appear  to  be  more  important  in  this  respect  than  the  amount  of 
water. 

(11)  In  the  case  of  the  polarized  spectra  of  the  double  chlorides,  both 
components  decay  at  the  same  rate  and  no  change  in  relative  bright- 
ness can  be  detected  throughout  the  range  covered  by  observation. 

PHOSPHORESCENCE  OF  LONG  DURATION. 

While  comparing  the  spectra  of  uranyl  salts  under  excitation  by 
kathode  rays  and  under  photo-excitation,  in  1917,  Misses  Wick  and 
McDowell  discovered  that  certain  salts  continued  to  glow  for  several 
minutes  after  bombardment  in  the  vacuum  tube,  at  the  temperature 
of  liquid  air. 

Many  uranyl  compounds  are  unstable  in  vacuo,  and  of  those  which 
are  not  decomposed  rapidly,  some,  notably  the  chlorides,  are  prac- 
tically inactive  under  the  kathode  rays.  The  following  salts,  which 
were  prepared  by  Mr.  Wilber  in  the  form  of  fairly  large,  well-formed 
crystals,  gave  bright  fluorescence  and  were  fairly  stable : 

Uranyl  potassium  nitrate,  K2U02(N03)4  (crystallized  from  10  to  30  per  cent  nitric 

acid). 
Uranyl  potassium  nitrate,  IGUOaCNOs)*  (long  crystals  from  2  to  3  per  cent  nitric 

acid). 
Uranyl  potassium  nitrate,  KU02(N03)3  (water  form). 
Uranyl  potassium  nitrate,  KU02(N03)8  (anhydrous). 
Uranyl  potassium  sulphate. 
Uranyl  potassium  sulphate  (with  2  molecules  of  water). 

An  examination  was  made  of  all  of  this  group.  They  were  found 
to  exhibit  phosphorescence  in  varying  degree.  Some  showed  no  phos- 
phorescence of  noticeable  duration.  The  following,  which  were  among 
the  brightest,  were  selected  for  study : 

(1  and  2)  K2U02(N03)4.  The  first  form.  A,  was  crystallized  from 
a  10  to  30  per  cent  solution  of  nitric  acid,  and  the  second  form,  B,  from 
a  2  to  3  per  cent  solution.  Although  the  crystallographic  form  is 
identical,  form  A  crystallizes  in  short,  thick  crystals  and  form  B  in 
long,  slender  crystals.  There  appeared  to  be  a  slight  difference  in  the 
phosphorescence  of  the  two  forms.  It  is  possible,  however,  that  the 
difference  observed  might  have  been  due  to  some  variation  in  the 
conditions  under  which  the  phosphorescence  was  produced. 

(3)  K2U02(S04)2.  To  ascertain  whether,  as  the  result  of  exposure 
to  the  kathode  rays,  the  surface  layer  of  the  crystals  had  undergone 
some  change  which  rendered  them  capable  of  persistent  phosphores- 
cence under  photo-excitation,  they  were  alternately  illuminated  by  the 
light  of  a  carbon  arc  and  bombarded  by  the  kathode  rays.    To  accom- 


PHOSPHORESCENCE   SPECTRA.  57 

plish  this  without  changing  any  conditions  except  the  mode  of  excita- 
tion the  tube  containing  the  crystal  under  observation  was  mounted 
within  an  unsilvered  cyUndrical  Dewar  flask  and  cooled  to  the  tempera- 
ture of  liquid  air.  Light  from  a  carbon  arc  was  focussed  upon  the 
crystal  through  the  walls  of  the  Dewar  flask  and  of  the  vacuum-tube, 
producing  intense  fluorescence,  but  there  was  no  after-glow  of  duration 
sufl&cient  to  be  detected.  The  kathode  discharge,  however,  caused  the 
persistent  phosphorescence  already  described  and  the  effect  appeared 
to  be  distinctly  cumulative,  requiring  excitation  for  several  seconds. 
After  the  phosphorescence  had  died  away,  photo-excitation  was  re- 
sumed, and  this  process  was  repeated  many  times  without  observable 
change  in  the  effect  of  the  light. 

IDENTITY  OF  THE  SPECTRA  DURING  FLUORESCENCE  AND  KATHODE- 
PHOSPHORESCENCE. 

To  determine  whether  the  spectrum,  during  this  persistent  phos- 
phorescence, corresponded  with  the  fluorescence  spectrum,  settings 
on  several  of  the  brightest  bands  were  made  with  the  Hilger  spec- 
troscope. The  result  was  the  same  as  the  observations  upon  the  brief 
phosphorescence  following  photo-excitation,  described  in  an  earlier 
paragraph  of  this  chapter;  ^.  e.,  the  spectra  were  found  to  be  identical 
during  and  after  excitation  and  remained  unchanged  in  character  as 
long  as  they  were  visible. 

CURVES  OF  DECAY  FOR  THE  KATHODE-PHOSPHORESCENCE. 

Misses  Wick  and  McDowell  also  determined  the  law  of  decay  for 
the  three  salts  (1,  2,  and  3)  selected  for  investigation.  Since  the  effect 
lasted  for  several  minutes,  it  was  possible  to  use  the  method  commonly 
employed  in  such  measurements.  The  arrangement  of  the  apparatus 
is  shown  in  figure  44. 


® 


> 


Fig.  44. 


A  Lummer-Brodhun  cube  A  was  placed  at  one  end  of  a  track  XYy 
about  3.5  meters  long.  The  crystal  B  was  placed  opposite  one  face  of 
the  cube.  The  comparison  source  L  was  a  5-volt  tungsten  lamp  placed 
in  parallel  with  a  suitable  rheostat  upon  a  55-volt  circuit.  The  lamp 
was  mounted  in  a  carriage  C,  running  on  the  track  XF,  on  which,  at 
intervals  of  about  25  cm.,  stops  were  placed.  Green,  blue,  and  ground 
glass  absorption  plates  P  and  P'  were  inserted  to  obtain  a  comparison 
source  of  the  proper  color  and  intensity.  A  chronograph  was  used 
to  record  the  time.  The  zero  of  time  was  in  every  instance  recorded 
when  the  primary  circuit  of  the  induction  coil  was  broken.    When  the 


58 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


intensity  of  phosphorescence  matched  that  of  the  source  in  the  first 
possible  position,  the  time  was  again  recorded  and  the  carriage  moved 
to  the  next  stop,  and  allowed  to  remain  until  a  match  was  made  as 
before.  This  procedure  was  continued  until  the  phosphorescence  was 
too  faint  to  observe  or  until  the  end  of  the  track  was  reached. 

The  interpretation  of  the  results  was  somewhat  difficult,  since  the 
instability  of  the  crystals  rendered  uncertain  both  the  control  of  the 
vacuum  and  the  maintenance  of  the  crystal  surface  unchanged  during 
prolonged  bombardment.  The  general  shape  of  the  decay  curve  after 
long  excitation  is  shown  in  figure  45.  The  curves  are  of  the  type  usual 
with  phosphorescence  of  long  duration,  consisting  of  two  linear 
processes,  of  which  the  first  is  the  more  rapid,  whereas,  as  has  been 
shown  in  the  previous  portions  of  this  chapter,  the  decay  following 
photo-excitation  is  of  a  new  and  entirely  different  type. 


ri 

; 

^ 

1 

/ 

/ 

/ 

V 

/ 

/ 

a/ 

.^ 

/ 

/ 

/ 

/ 

/ 

/ 

/ 

1 

/ 

0/ 

/ 

/ 

^y 

>■■ 

A 

i 

^ 

^ 

/ 

/ 

/ 

> 

X 

. 

Jfy/^ 

K 

/ 

// 

y 

Y 

]j 

r 

i 

SIC 

4 
JHO$ 

00 

K 

>6 
SKCO 

1< 
MDS 

^ 

K 

SE< 

:o«s* 

M 

« 

M 

Fig.  45. 


Fio.  46. 


Fia.  47. 


Under  different  conditions,  phosphorescence  was  observed  to  last 
from  less  than  a  minute  to  10  or  15  minutes.  The  exact  form  of  the 
curve  varied  with  the  time  of  excitation.  The  time  of  decay  was  found 
to  increase  with  the  time  of  excitation,  as  shown  in  figure  46,  but  the 
initial  brightness  changed  relatively  little.  There  was  some  evidence  to 
indicate  that  under  similar  conditions  of  vacuum  the  rate  of  the  first 
process  remained  practically  unchanged  for  varying  times  of  excita- 
tion, but  that  the  second  process  began  sooner  for  longer  excitation, 
as  shown  in  figures  47  and  48.  In  figure  48,  curves  1  and  2,  obtained 
by  a  short-time  excitation,  show  only  the  first  process,  whereas  curves 
45  and  46,  obtained  by  excitations  of  40  and  80  seconds  respectively, 
indicate  that  a  state  of  saturation  had  been  reached  such  that  added 
excitation  produced  no  change  in  the  phosphorescence. 

As  has  been  stated,  the  initial  brightness  and  rate  of  decay  were 
found  also  to  depend  upon  the  strength  of  the  bombardment,  as  varied 
by  the  pressure  in  the  tube  and  by  the  voltage  applied  to  the  induction 


PHOSPHORESCENCE   SPECTRA. 


59 


coil.  The  curves  of  figure  45,  for  example,  were  obtained  with  a  rela- 
tively high  vacuum,  whereas  those  of  figure  49  were  obtained  with  a 
very  low  vacuum,  so  that  the  decay  was  comparatively  rapid  and  there 
was  only  a  suggestion  of  the  beginning  of  the  second  process  in  the 
position  of  the  last  point  observed.^  Slight  changes  in  temperature, 
such  as  were  produced  when  the  liquid  air  fell  below  the  line  of  the 
crystal,  were  found  also  to  produce  changes  in  the  initial  brightness  and 
rate  of  decay. 


ri 

1 

I 

3, 

• 

•AA 

/ 

^a*^ 

• 

^ 

/ 

f 

^ 

^ 

^ 

*MA 

.0 

A 

^* 

/ 

r 

25 


50  75 

SICONDS 

Fig.  48. 


100 


To  determine  whether  the  excitation  produced  any  secondary  change 
in  the  crystal,  which  persisted  after  the  phosphorescence  had  dis- 
appeared, so  that  there  would  be  a  progressive  building  up  of  the 
phosphorescence,  excitations  were  made  of  equal  length,  repeated  at 
as  nearly  equal  intervals  as  decay  observations  permitted.  Figure  49 
shows  that,  at  a  fairly  low  cathode  vacuum,  an  excitation  of  20  seconds, 
repeated  at  approximately   1-minute  intervals,  produced  identical 


d 

/f 

100 

i              ri 

^/ 

A 

JOC 

^y 

y 

A 

nT 

y 

x: 

MUt 

100 

/ 

y 

y 

y 

y 

i/^— 

/^ 

1 

0 

1 2 

fe-' 

'  i 

6 

1 

M) 

1)0 

SfiCONDS 
Fig.  49. 


SECONDS 

Fig.  50. 


decay  curves.  The  same  effect  is  shown  in  figure  50  for  a  much  longer 
period  of  decay.  When  the  time  between  excitations  was  short  as 
compared  to  the  time  and  strength  of  excitation,  there  appeared  to  be 
a  progressive  change,  as  indicated  in  figure  51. 


60 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


From  this  investigation  by  Misses  Wick  and  McDowell,  two  definite 
conclusions  may  be  drawn : 

(1)  The  spectrum  of  the  long-time  phosphorescence  produced  by 
cathode-ray  excitation  at  liquid-air  temperatures  is  identical  with  the 
fluorescence  spectrum. 


1-5 

/" 

.^ 

^ 

J 

/ 

h 

/ 

If/ 

•V 

too 


Fig.  51. 


(2)  The  decay  curve  of  the  cathode  phosphorescence  differs  in  the 
most  striking  manner  from  that  of  the  brief  photo-phosphorescence. 
It  corresponds  in  type  with  that  usually  found  in  cases  of  phosphores- 
cence of  long  duration. 


V.  THE  MORE  INTIMATE  STRUCTURE  OF  URANYL  SPECTRA 
AS  REVEALED  BY  COOLING. 

It  was  first  shown  by  J.  and  H.  Becquerel  and  Onnes,^  who  studied 
the  spectra  of  several  of  the  uranyl  salts  when  excited  to  fluorescence 
at  the  temperature  of  liquid  air  and  ultimately  at  that  of  hquid  hydro- 
gen, that  each  band  of  the  spectrum  as  we  know  it  at  +20°  is  resolved 
into  a  group  of  much  narrower  bands.  It  was  further  shown  by  these 
investigators  that  all  of  the  various  groups  of  bands  in  a  given  spectrum 
were  resolved  in  precisely  the  same  manner,  the  homologous  com- 
ponents forming  series. 

This  more  intimate  structure,  which  is  revealed  by  cooling,  may  be 
studied  to  great  advantage  in  the  case  of  the  double  chlorides,  which 
s^lts,  as  has  been  noted  in  Chapter  III,  have  spectra  sufficiently 
resolved  at  +20°  so  that  the  origin  of  the  components  observed  at 
— 185°  can  be  traced  and  the  relation  of  the  two  spectra  to  one  another 
much  more  definitely  determined  than  is  the  case  where  the  spectrum 
at  +20°  consists  of  unresolved  bands. 

Four  of  these  chlorides  have  the  following  composition: 

UO2CI2. 2KCI+2H2O.  U02Cl2.2RbCl+2H20. 

UO2CI2. 2NH4CI+2H2O.  UO2CI2.2CSCI. 

They  crystallize  in  triclinic  plates  which  are  strongly  fluorescent 
and  their  spectra,  which  are  almost  identical  in  structure,  are  resolved 
at  room  temperature  into  8  groups  of  narrow  bands.  Each  group, 
which  corresponds  to  a  single  band  of  the  ordinary  uranyl  fluorescence 
spectrum,  consists  of  5  nearly  equidistant  bands.  The  symmetry  of 
these  spectra,  as  they  appear  to  the  eye  when  viewed  with  a  spectro- 
scope of  moderate  dispersion,  is  most  striking.  The  bands  are  well 
separated  from  their  neighbors  and  are  about  one-tenth  as  wide  as  the 
bands  of  the  ordinary  type  of  uranyl  spectra. 

The  distribution  of  intensities  within  the  group  has  been  determined 
for  the  visually  brightest  group  in  the  spectrum  of  the  ammonium 
uranyl  chloride  by  means  of  the  spectrophotometer.  The  results  of 
such  a  determination  are  given  in  table  18,  and  are  shown  graphically 
in  figure  52. 

The  curve  (fig.  52)  which  forms  an  envelope  of  the  group  of  bands  is 
of  the  same  type  as  that  for  the  distribution  of  intensities  in  a  single 
band  of  the  ordinary  uranyl  fluorescence  spectrum  and  of  the  envelope 
of  the  set  of  bands  in  such  a  spectrum  and  is  also  similar  to  curves  of 
distribution  of  the  fluorescent  spectra  having  a  single  broad  band.^ 

The  effect  of  cooling  is  likewise  analogous,  the  envelope  for  —185® 
being  narrower  on  account  of  the  great  relative  reduction  in  brightness 
of  the  outlying  members  of  the  group.    All  the  bands  are  shifted  in 

^  Becquerel  and  Onnes,  Leiden  Communications,  110.     1909. 
*  See  Chapters  II  and  III. 

61 


62 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  18. — Intensities 
of  hands  in  group  6 
{excited  at  +20°  C). 


Band. 

Intensity. 

5306m 

18 

5259 

33 

5208 

24 

5159 

11 

5119 

(0 

Visible,  but  too  dim  for 
spectrophotometric 
measurement. 


position  as  well  as  changed  in  intensity  in  a  manner  to  be  described  in 
a  subsequent  paragraph. 

To  determine  as  closely  as  possible  the  wave-lengths  of  the  bands, 
photographs  of  the  spectra  of  the  four  double  chlorides  were  taken 
and  many  visual  settings  were  made.  Fluorescence  was  excited  by 
means  of  the  carbon  arc,  the  light  from  which  passed  through  a  screen 
opaque  to  rays  of  wave-length  greater  than  about  0.45  ju  and  was 
f  ocussed  upon  the  crystal.  Various  exposures  were 
employed  on  account  of  the  great  d  fferences  in  the 
intensity  of  the  bands  and  special  plates  were  used 
for  the  red  end  of  the  spectrum.  The  exciting 
light  was  excluded  from  the  camera  by  the  use  of 
suitable  screens  opaque  to  the  blue  and  violet  except 
where  the  absorption  spectrum  was  to  be  recorded. 

The  various  negatives  were  measured  by  mount- 
ing them  on  a  micrometer  stage  in  the  field  of  the 
lantern.  The  micrometer-screw  was  carefully  cali- 
brated, so  that  wave-lengths  could  be  determined  by 
measuring  the  distance  of  the  crests  of  the  bands 
from  certain  reference  lines  of  the  mercury  spectrum,  which  was  photo- 
graphed on  each  negative  so  as  to  overlap  the  fluorescence  spectrum. 

This  method  of  projection  was 
found  better  than  the  use  of  the 
comparator  commonly  employed  in 
the  measurement  of  line  spectra, 
because  of  the  hazy  character  of  the 
bands  and  because  bands  that  are 
so  weak  and  vague  as  to  be  invis- 
ible even  under  a  low-power  micro- 
scope could  be  seen  and  located  by 
means  of  the  lantern.  Many 
measurements  of  the  stronger  bands 
were  made  with  the  comparator  as 
a  check  on  the  determinations  with 
the  lantern. 

These  measurements  confirmed 
to  a  remarkable  degree  the  apparent 
symmetry  of  the  spectrum.  When 
all  the  bands  are  plotted  on  a  large 
scale,  in  a  diagram  with  the  recip- 
rocal of  wave-lengths  as  abscissae, 
the  spectrum  is  seen  to  consist  of  8 
groups  of  5  bands  each,  as  already  described.  The  nearly  uniform 
arrangement  of  the  bands  of  each  group  repeats  itself  precisely  from 
group  to  group,  so  that  corresponding  members  of  the  groups  form  an 


.52 


53^ 


Fig.  52. 


INTIMATE   STRUCTURE   ON   COOLING. 


63 


homologous  series  of  equidistant  bands.  This  interval,  moreover,  is 
very  nearly  the  same  for  all  five  of  these  homologous  series;  but 
although  the  departures  from  equahty  are  of  the  same  order  as  the 
errors  of  measurement,  there  is  reason,  as  will  be  seen  later,  to  regard 
them  as  real. 

The  general  arrangement  of  the  bands  in  these  spectra  is  roughly 
depicted  in  figure  53,  which  is  based  upon  measurements  of  the  fluores- 
cence spectrum  of  the  ammonium  uranyl  chloride.  Horizontal  dis- 
tances are  plotted  on  the  scale  of  frequencies,  the  corresponding  wave- 


lengths being  indicated  for  convenience.  Vertical  heights  indicate 
relative  intensities,  but  with  some  pretence  of  accuracy.  The  first 
and  eighth  groups  at  the  extreme  left  and  right,  for  example,  if  drawn 
to  scale,  would  be  scarcely  visible.  They  are,  in  fact,  so  feeble  that 
they  can  be  observed  only  with  the  greatest  difficulty.  The  location 
of  the  various  bands  of  the  4  double  chlorides,  in  wave-lengths  and  in 
frequencies  (l/ju  X  10^)  is  given  in  table  29  at  the  end  of  this  chapter. 
The  values  given  are  the  averages  of  several  readings  from  the  photo- 
graphs and  from  visual  settings.  The  bands  in  each  group  from  the 
red  toward  the  violet  are  designated  by  the  letters  5,  C,  D,  E,  and  A, 
and  bands  having  the  same  letter  thus  form  homologous  series. 

To  determine  the  intervals  between  groups,  the  position  of  what 
may  be  called  the  center  of  each  group  was  found  by  averaging  the 
frequencies  of  all  5  bands.  The  intervals  between  these  centers  for 
groups  2,  3,  4,  5,  6,  and  7  are  given  in  table  19.  Groups  1  and  8,  for 
which  insufficient  data  were  available,  were  omitted,  except  in  the 
case  of  the  ammonium  chloride. 

The  only  indication  of  a  systematic  departure  from  uniformity  of 
interval  for  a  single  salt  appears  in  the  case  of  the  caesium  chloride,  the 
average  group-interval  for  which  is  smaller  than  that  of  the  other  salts 
by  nearly  0.5  per  cent. 


64 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


As  will  appear  in  the  course  of  the  subsequent  consideration  of 
individual  series,  the  tendency  of  the  group  intervals  of  the  caesium 
salt  to  diminish  toward  the  violet  is  not,  as  might  seem  at  first  sight, 
an  indication  that  the  groups  are  made  up  of  series  having  a  diminish- 
ing interval.  As  regards  the  other  salts,  it  will  be  noted  that  the  dis- 
tance  between  groups  is  essentially  constant. 


Table  19. — Distances  between  fluorescence 

groups. 

Group. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Cfesium 
uranyl  chloride. 

Center  of 
group. 

Inter- 
val. 

Center  of 
group. 

Inter- 
val. 

Center  of 
group. 

Inter- 
val. 

Center  of 
group. 

Inter- 
val. 

1. 
2. 
3. 
4. 
5. 
6. 
7. 

1505.3 
1588.6 
1671.9 
1755.0 
1838.4 
1922.3 
2005.6 

1587.2 
1670.8 
1754.0 
1836.6 
1919.6 
2003.3 

"83.6" 

83.2 
82.6 
83.0 
83.7 

83.3 
83.3 
83.1 
83.4 
83.9 
83.3 

1591.5 
1674.9 
1758.3 
1840.7 
1924.2 
2007.8 

'"83!4" 
83.4 
82.4 
83.5 
83.6 

1592.6 
1675.9 
1759.3 
1841 . 8 
1924.7 
2006.6 

83.3 
83.4 

82.5 
82.9 
81.9 

Average  disU 

mcea .... 

83.22 

83.38 

83.26 

82.80 

DISTRIBUTION  OF  BANDS  WITHIN  THE  GROUPS. 

While  to  the  eye  the  fluorescence  spectra  under  consideration  present 
the  appearance  of  evenly  spaced  bands  varying  periodically  in  intensity 
so  as  to  form  the  groups,  this  is  not  strictly  the  case,  as  may  readily  be 
shown  by  subtracting  neighboring  values  in  table  29.  The  average 
distances  thus  obtained  are  given,  for  convenience,  in  table  20. 

The  greatest  departures  from  uniformity  of  distribution  occur  in  the 
spectra  of  the  rubidium  chloride  and  the  caesium  chloride. 

Table  20. — Average  distances  between  neighboring  bands  in  the  fluorescence  spectrum  at  -{-20°  C. 


Fluorescing 
substances. 

Distances  between  bands. 

C  to  B. 

D  to  C. 

E  to  D. 

A  to  E. 

B  to  A. 

UO2CI2.2KCI 

UO2CI2.2NH4CI.... 

U02Cl2.2RbCl 

UO2CI2.2C3CI 

Averages 

15.97 
17.56 
16.20 
18.25 

18.66 
17.74 
18.43 
12.85 

17.96 
17.86 
18.50 
18.63 

14.70 
15.67 
12.75 
14.52 

15.58 
15.67 
17.12 
18.10 

16.99 

16.92 

18.24 

14.41 

16.62 

In  the  rubidium  spectrum,  bands  A  and  E  are  crowded  together, 
the  average  interval  being  12.75,  and  in  the  caesium  spectrum  D  and  C 
are  similarly  crowded.  It  will  be  noted  that  the  average  distance 
between  A  and  E  is  less  for  the  four  chlorides  than  any  of  the  corre- 
sponding distances  between  other  bands. 

The  arrangement  of  the  bands  within  the  group  in  the  four  salts  is 
conveniently  compared  by  means  of  the  diagram  in  figure  54,  in  which 


INTIMATE    STRUCTURE   ON   COOLING. 


65 


the  geometrical  centers  of  the  groups  are  in  the  same  vertical  line.    It 
will  be  seen  from  the  diagram : 

(1)  That  the  group  center  is  in  all  four  cases  almost  coincident  with 
the  crest  of  the  D  band. 

(2)  That  the  distance  between  D  and  E  is  approximately  the  same 
in  all. 

(3)  That  the  arrangement  of  bands  within  the  group  is  essentially 
the  same  in  all,  except  for  the  displacement  of  band  A  in  the  spectrum 
of  the  rubidium  and  of  B  and  C  in  that  of  the  csesium  salt,  as  mentioned 
above. 

Further  discussion  of  these  discrepancies  will  be  found  in  a  later 
paragraph  of  this  chapter. 

INTERVALS  OF  THE  INDIVIDUAL  SERIES. 

For  the  consideration  of  the  frequency  intervals  of  the  individual 
series,  the  values  from  table  29  have  been  arranged  by  series  in  table 
30.  Distances  between  the  observed  positions  of  neighboring  members 
of  each  series  are  given  in  the  column  marked  ''Intervals."  To 
facilitate  the  detection  of  systematic  departures  from  uniformity  of 
interval,  a  column  of  values  calculated  by  the  following  method  is 
likewise  given:  A  ''center"  for  each  group  was  found  in  the  manner 
already  employed  for  determining  the  group  centers.  Around  this  the 
calculated  positions  were  arranged  under  the  assumption  of  a  con- 
stant frequency  interval  equal 
to  the  average  of  the  observed 
intervals  for  each  series  sepa- 
rately. The  column  marked 
' '  Differences ' '  indicates  the  de- 
parture of  the  observed  values 
from  those  thus  calculated. 
The  departures  from  uniform- 
ity of  interval  are  unsyste- 
matic, indicating,  for  all  the 
salts,  that  the  series  may  he  regarded  as  having  a  constant  frequency  interval 

This  interval  has  been  computed  for  each  series  by  subtracting  the 
observed  frequency  of  each  band  from  the  frequencies  of  all  the  other 
bands  of  the  series  and  dividing  the  sum  by  the  total  number  of  inter- 
vals in  question.    The  results  are  presented  in  table  21. 

These  data  indicate  no  progressive  change  of  interval  with  the 
molecular  weight,  except  that  the  interval  is  definitely  smaller  for  the 
csesium  uranyl  chloride.  The  other  three  salts,  so  far  as  this  deter- 
mination goes,  must  be  regarded  as  having  the  same  average  interval. 
It  is  likewise  difficult  to  distinguish  with  certainty  differences  in  the 
intervals  of  different  bands  in  a  given  salt,  except  that  the  C  band  has 
in  general  a  smaller  interval  than  the  other  series,  or  of  a  given  band 
in  the  different  salts,  excepting  in  the  case  of  the  caesium  chloride. 


B 
K 

C 

:          c 

1 

1 

)              E 

y 

\ 

NH4 

1         i 

Rb 

Cs 

1 
1 

40 

2.0                   0                   20                 4.0    1 

Fig.  54. 


66 


FLUORESCENCE   OF  THE   URANYL    SALTS. 


At  the  same  time,  while  not  obviously  systematic,  the  variations 
in  these  values  are  considerably  larger  than  those  resulting  from  the 
measurement  of  the  interval  of  any  given  series,  taken  by  itself,  which 
should  not  exceed,  at  most,  0.2. 

Table  21. — Average  intervals  at  -\-W°  C.  for  the  four  double  chlorides. 


Series. 

K. 

NH4. 

Rb. 

Cs. 

Av.  by 
series. 

B 

C 

D 

E 

A 

Av... 

83.42 
83.11 
83.30 
83.00 
83.23 

83.34 
82.99 
83.21 
83.81 
83.65 

83.49 
82.97 
83.17 
82.97 
83.77 

82.32 
82.50 
82.85 
83.45 

82.85 

83.14 
82.89 
83.13 
83.31 
83.37 

83.21 

• 

83.40 

83.27 

82.80 

83.17 

These  seeming  discrepancies  are  not  to  be  considered  as  wholly 
accidental,  but  as  being  due  to  the  fact  that  the  bands  are  complex, 
and  variously  so^,  as  will  appear  from  the  study  of  these  spectra  at  low 
temperatures. 

While  he  determinations  thus 
far  described  may  be  regarded  as 
indecisive  as  to  small  differences 
of  interval  between  the  various 
series  and  salts,  excepting  as 
noted  above,  the  influence  of 
molecular  weight  upon  the  posi- 
tion of  bands  in  the  spectrum  is 
unmistakable. 

In  tables  29  and  30  (at  end  of 
chapter)  the  almost  universal 
and  fairly  regular  increase  in  the 
frequency  of  each  band  as  we 
pass  from  potassium  to  caesium  is 
sufficiently  evident.  In  figure 
55  this  general  shift,  which  is 
present  in  all  the  groups  and 
affects  all  series,  can  be  seen  at 
a  glance.  Almost  the  only  re- 
versed shifts  occur  in  the  case  of 
those  bands  of  the  caesium  spec- 
trum which  show anomolous  plac- 
ing in  the  spectral  groups 

In  table  19,  where  the  groups 
are  units,  the  accidental  errors 

pertaining  to  individual  bands  are  submerged  in  the  processes  of  aver- 
aging and  the  shift  with  molecular  weight  appears  as  a  still  more 


1   -r-      1        I        1        1        1        1 

^    15          16         17         18         19         20         21 

SERIES 

B 

K     1          1          1           1          1           1           1 

NH.I          1           i           1          t           i           1 

Rb  1       1        1       1       1       1       1 

Cs     1          1           1          1          1          1          1 

C 

K        1          1          I          1          1          1          1 

NH.  1          1          1          1          I          1          1 

Rb     1         1        1        1        1        1        1 

Cs       1          1          1          1          1          1          1 

D 

K           1          1          1          1          1          1 

NH.     1          1          1          1          1          1 

Rb       1        1        1        1        1        1 

Cs         1          1          1          1          I          1 

E 

K            1          I          I          1          1          1 

NH.       1          1           1          1          1          1 

Rb           i          1          1          1          1          1 

Cs           1          1           1          1          1          1 

A 

K              1          1          1          1          1          1 

NH4         1          I          1          1          1          1 

Rb            1          1          1          1          i          1 

Cs            1          1          1          1          1          i 

'^          %^^f^              '^^^                    -^^^ 

INTIMATE    STRUCTURE   ON   COOLING.  67 

systematic  phenomenon.  Ignoring  group  7,  in  which  the  bands  are 
displaced  by  absorption  in  a  manner  to  be  discussed  later,  we  find  the 
following  shifts  to  exist. 

Table  22.— Shift  of  the  groups. 

Group 2  3  4  5  6 

Shift 5.4        5.1         5.3        5.2        5.1 

Average  shift  from  K  to  Cs,  5.2 

Ths  shift  is  therefore  to  be  regarded  as  approximately  uniform 
throughout  the  spectrum.  The  shift  is  much  greater  between  NH4  and 
Rb  than  in  the  other  cases,  the  averages  being  as  shown  in  table  23. 

Table  23. — Average  shift  of  groups. 

K-NH4 1.6 

NH4-Rb 2.7 

Rb-Cs 9 

It  will  be  noticed  that  in  this  discussion  the  order  of  molecular 
weights  used  is  K,  NH4,  Rb,  Cs — NH4  being  placed  between  K  and 
Rb  instead  of  in  its  proper  position.  This  is  in  accordance  with  the 
results  of  Tutton,^  who  has  shown  that  in  various  optical  properties  of 
crystals  which  depend  on  the  molecular  weights,  NH4  always  lies 
between  K  and  Rb,  as  though  its  effective  molecular  weight  were 
larger  instead  of  being  smaller  than  K. 

THE  EFFECTS  OF  TEMPERATURE. 

The  narrow,  line-like  bands  into  which  the  ordinary  uranyl  spec- 
trum is  resolved  at  low  temperatures^  form  a  rather  complex  aggre- 
gation separable  into  a  series  of  identically  arranged  groups  corre- 
sponding to  the  unresolved  bands  at  +20°,  but  related  to  the  over- 
lapping components  of  the  latter  in  a  manner  not  easily  capable  of 
direct  determination.  It  was  deemed  of  especial  interest,  therefore,  to 
observe  the  effect  of  cooling  on  the  double  chlorides,  where  the  relation, 
owing  to  the  partial  resolution  at  +20°,  should  be  more  obvious. 

For  this  purpose  a  crystal,  C,  of  the  salt  to  be  examined  was  mounted 
within  a  long  cylindrical  Dewar  flask,  D,  with  unsilvered  walls  (fig.  56). 
The  carbon  arc  A  was  focussed  on  the  crystal  by  the  lens  L.  A  water- 
cell  W  was  inserted  between  the  arc  and  the  condenser.  The  fight- 
filter  F  was  opaque  to  all  but  the  violet  and  ultra-violet  rays  used  for 
excitation.  Observations  with  the  Hilger  spectroscope  H,  a  portion 
of  the  coUimator  of  which  is  shown,  were  made  through  a  second  filter 
E  opaque  to  the  exciting  fight  but  transmitting  the  fluorescence.  The 
arc  and  specimen  were  well  screened  by  an  opaque  box  BB.  When 
it  was  desired  to  photograph  the  spectrum  a  camera  was  substituted 
for  the  observing  telescope  of  the  spectrometer. 

The  control  and  adjustment  of  temperature  were  effected  by  attach- 
ing the  crystal  at  the  upper  end  of  a  vertical  copper  rod  which  could  be 

^  Tutton,  A.  E.,  Crystalline  Structure  and  Chemical  Constitution.     (London,  1916.) 
'  See  Becquerel  and  Onnes,  1.  c. 


68 


FLUORESCENCE    OF   THE    URANYL    SALTS. 


immersed  more  or  less  deeply  in  the  liquid  air  by  raising  or  lowering 
the  Dewar  flask.  To  preclude  the  gathering  of  frost  or  moisture  on  the 
surface  of  the  crystal,  it  was  kept  during  the  entire  experiment  at  a 
sufficient  distance  below  the  lip  of  the  flask,  where  it  was  surrounded 
with  the  dry  atmosphere  above  the  slowly  evaporating  mass  of  liquid 
air.  Measurements  of  the  temperature  were  by  means  of  a  small  coil 
of  fine  copper  wire  mounted  at  the  same  level  as  the  crystal,  so  as  to 
have  always,  as  nearly  as  possible,  the  temperature  of  the  latter. 
Changes  in  the  resistance  of  the  coil  were  indicated  on  the  sheet  of  a 
Callender  recorder,  carefully  calibrated  to  read  directly  in  degrees 
centigrade  and  adjusted  for  a  range  from  +20°  to  —200°. 


B 
H 

1 

r 

D 

<  /\             \ 

\ 

/ 

F 

Wl             1 

A 

X 

a 

•]e$ 


A  A 


Fig.  56. 


Fig.  57. 


The  crystal  was  mounted  so  as  to  cover  a  transverse  slot  in  the 
copper  rod.  It  could  thus  be  illuminated  either  from  the  front,  as 
shown  above,  or  from  behind  by  fight  transmitted  through  the  slot. 
The  latter  arrangement  was  employed  especially  in  the  study  of  the 
absorption  spectrum. 

When  the  substance,  excited  to  fluorescence  in  the  manner  already 
described,  was  gradually  cooled  to  the  temperature  of  liquid  air  and 
the  spectrum  was  observed  through  the  Hilger  spectrometer,  the  fol- 
lowing changes  were  noted: 

(1)  The  bands  become  narrower  and  better  defined  until  at  the 
temperature  of  liquid  air  they  correspond  in  appearance  to  the  usual 
line-like  bands  characteristic  of  the  fluorescence  spectra  of  the  uranyl 
salts  at  low  temperatures. 

(2)  As  the  temperature  falls  the  bands  are  gradually  resolved  into 
doublets.  One  component  of  each  doublet  becomes  rapidly  brighter, 
while  the  other  frequently  becomes  more  indistinct  and  sometimes 
disappears.     The  general  effect  is  that  of  a  shift  toward  the  violet 


INTIMATE   STRUCTURE   ON   COOLING,  69 

amounting  to  about  a  third  of  the  distance  between  the  original  bands. 
The  nature  of  this  apparent  shift  is  as  follows : 

Each  band  at  +20°  may  be  regarded  as  an  unresolved  doublet,  of 
which  in  general  the  member  of  longer  wave-length  is  relatively  so 
much  the  stronger  that  its  position  determines  approximately  the 
location  of  the  crest  of  the  composite  band  (see  fig.  57).  The  effect  of 
cooling  is  to  resolve  this  doublet  into  separately  distinguishable  bands 
and  at  the  same  time  to  cause  a  subsidence  of  the  stronger  and  an 
increase  of  the  weaker  member.  The  member  of  the  shorter  wave- 
length usually  becomes  dominant  at  low  temperatures,  and  in  so  far  as 
this  occurs  the  arrangement  of  the  spectrum  appears  to  be  undis- 
turbed but  shifted  toward  the  violet  by  an  amount  representing  the 
width  of  the  doublet.  There  are,  however,  certain  exceptions  to  this 
rule,  so  that  the  relation  of  the  resolved  spectrum  to  that  at  +20°  is 
not  so  simple  as  the  above  description  would  imply.  The  appearance 
of  the  group,  if  this  be  its  real  structure  (i.  e.,  a  set  of  nearly  equi- 
distant doublets,  the  distance  between  the  members  of  all  the  doublets 
being  nearly  the  same),  would  then  be  as  shown  in  figure  57. 

At  +20°,  B',  C,  D\  E\  and  A'  are  entirely  concealed  by  the  over- 
lapping of  the  bands.  At  — 185°,  B,  C,  D\  E,  and  A  may  or  may  not 
be  visible,  according  to  their  intensity  or  the  completeness  of  the  resolu- 
tion, which  in  fact  varies  greatly  in  different  parts  of  the  spectrum. 

It  will  be  noticed  that  in  the  lower  diagram  in  figure  57,  D  and  not 
D'  is  the  dominant  component.  This  is  a  condition  which  obtains  in 
the  ammonium  chloride,  with  the  result  that  C  and  D,  which  appear 
to  have  replaced  the  strong  C  and  D  bands  of  the  spectrum  of  +20°, 
are  near  together,  D  and  E'  far  apart,  and  the  symmetry  of  the  group 
is  impaired.  Similar  complications  occur  Ukewise  in  the  spectra  of  the 
other  double  chlorides. 

To  illustrate  the  application  of  this  assumption,  the  spectrum  of  the 
ammonium  uranyl  chloride  has  been  mapped  in  the  manner  shown 
in  figure  58,  in  which  the  fluorescence  bands  of  the  8  groups  as  they 
occur  at  — 185°  are  shown  in  their  relation  to  a  hypothetical  grouping 
given  at  the  head  of  the  diagram.  This  grouping  consists  of  the  set  of 
imagined  doublets  of  which,  as  in  a  previous  paragraph,  the  spectrum 
at  +20°  is  supposed  to  be  made  up.  The  spacing  for  each  doublet  is 
that  determined  from  the  observed  average  shift  on  cooling  and  the 
relative  divergence  from  this  arrangement  is  shown  for  all  the  bands 
of  each  group. 

A  scrutiny  of  the  fluorescence  spectrum  at  -185°,  group  by  group, 
by  means  of  this  diagram,  affords  very  satisfactory  confirmation  of 
this  hypothesis  concerning  the  apparent  shift.    It  is  obvious: 

(1)  That  not  all  the  components  B,  C,  D,  E,  and  A  will  necessarily  be 
visible  in  every  group  of  the  resolved  spectrum. 


70 


FLUORESCENCE    OF  THE   URANYL   SALTS. 


(2)  That  lack  of  resolution  in  any  region  may  give  the  appearance  of 
a  single  band  with  intermediate  crest  in  place  of  the  doublet. 

(3)  That  the  position  of  crests  of  the  unresolved  doublets  at  +20° 
will  not  necessarily  coincide  exactly  with  that  of  either  component. 

Bearing  these  points  in  mind,  it  will  be  seen  that  were  resolution 
complete  all  the  observed  bands  of  the  spectrum  at  —185°  would 
probably  fall  into  the  system  proposed  above. 

We  may  imagine  that  the  difference  between  the  resolution  of  the 
bands  C  and  D,  for  example,  as  seen  in  figure  54,  is  produced  by  changes 

in  the  unresolved  doublets  at 
+20°  when  the  temperature 
is  reduced  to  —185°,  of  the 
kind  indicated  in  figure  59. 
The  doublet  CC  forms  a 
single  band  with  crest  nearly 
coincident  with  C  at  +20°, 
and  this  owing  to  the  sub- 
sidence of  C  and  growth  of 
C  takes  the  resolved  form 
shown  at  — 185°.  In  the  case 
of  Z),  however,  the  unresolved 

c' 

A 


B 

b' 

i 

< 

'  "r  ir tf 

1    1    . 

r     1 

1    1  . 

1 

1    1  . 

1 

II   1  . 

1       . 

II   1  . 

1       . 

II   1  . 

1       1 

1  1  1 1  . 

1 

1 1  1  1 

A 


Fig.  58. 


-20  -185  -20       -185 

Fio.  59. 


band  has  an  intermediate  crest  at  D,  but  is  really  composed  of  over- 
lapping components  D'  and  D"  which  are  separately  visible  at  — 185°. 

The  wave-lengths  and  frequencies  of  the  bands  in  the  resolved 
spectra  of  the  four  double  chlorides,  as  observed  when  excited  at  the 
temperature  of  liquid  air,  are  given  in  table  31  at  the  end  of  the  chapter. 
The  nomenclature  used  in  this  and  subsequent  tables  is  chosen  to 
indicate  as  far  as  possible  the  relation  of  the  bands  at  — 185°  to  those 
at  +20°.  Thus  ^i,  B2,  etc.,  denote  components  of  B,  etc.,  which  have 
been  rendered  visible  by  the  resolution  effected  by  cooling. 

The  explanation  offered  above  to  account  for  the  relation  between 
the  spectra  at  +20°  and  at  —185°,  and  which  was  illustrated  in  the 
case  of  the  ammonium  uranyl  chloride  (see  fig.  58),  was  confirmed  by 
observations  upon  the  spectrum  of  that  salt  at  intermediate  tempera- 
tures.   It  was  thus  possible  to  watch  the  gradual  appearance  of  the 


INTIMATE   STRUCTURE   ON   COOLING. 


71 


components  characteristic  of  the  spectrum  at  low  temperatures  and  the 
simultaneous  fading  away  of  those  dominant  at  +20°.  The  same 
explanation  applies  equally  well  to  the  potassium  and  rubidium  double 
chlorides.  In  the  case  of  caesium  uranyl  chloride  the  relations  are 
complicated  by  the  further  resolution  of  these  components,  so  that  the 
connection  with  the  original  complexes  is  less  easily  traced. 

To  indicate  the  general  character  of  these  resolutions  and  the 
apparent  temperature  shift  which  results  therefrom,  the  positions  of 
the  bands  of  group  6  at  -185°  are  plotted  for  all  four  chlorides  (see 
fig.  60).  Intensities  of  the  —185°  bands  are  indicated  roughly  by  the 
height  of  the  Hues.  The  corresponding  crests  of  the  bands  at  +20° 
are  represented  by  dotted  Unes.  Group  6  was  selected  because  it 
offers  better  examples  of  the  further  breaking-up  of  the  components 
and  of  other  phases  of  the  process  of  resolution  than  do  groups  toward 
the  red  in  which  resolution  is  progressively 
less  complete. 

Two  questions  which  were  left  undetermined 
in  the  study  of  the  spectra  at  +20°  may  be 
regarded  as  settled  by  these  measurements  of 
the  bands  at  -185°. 

(1)  That  the  intervals  are  not  the  same 
for  all  series  in  a  given  spectrum  is  clearly 
established.  For  example,  the  components 
C],  C2,  which  take  the  place  of  the  C  bands  in 
all  four  spectra,  have  distinctly  different  in- 
tervals, i,  e.,  84.00  for  Ci  and  82.75  for  C2.  It 
noteworthy  that  C2,  which  becomes  the 


«•"  i     i   "i     i    \ 

B       C  ^2  D        E       A 


IS 


tlj 


n 


i  u, 


+20 


■.^nh 


* 


Cs 

-185° 


+20' 


ri 


1900 

Fig.  60. 


r 
I    I 

T955" 


crest  of  the  group  in  place  of  C  also,  has  the 

small  interval.      It   might    be    questioned 

whether  these  so-called  components  are  not 

merely  accidental  neighbors  rather  than 

products  of  the  same  vibrating  system,  but  for  the  fact  that  they 

are  present  in  all  the  spectra  and  have  very  nearly  if  not  precisely  the 

same  relative  positions  to  each  other  in  all. 

(2)  The  average  interval  of  all  series  in  the  spectrum  of  the  caesium 
chloride  (82.80)  at  +20°,  which  causes  the  notable  displacement  of  the 
bands  of  that  substance,  becomes  83.44  when  we  take  the  average  of 
the  intervals  of  the  bands  at  — 185°.  That  is  to  say,  it  is,  within  the 
errors  of  observation,  the  same  as  the  general  average  for  the  other 
salts.  On  the  basis  of  the  measurements  at  low  temperatures  (see 
table  24),  we  must  conclude  that  the  four  double  chlorides  have  approx- 
imately the  same  average  frequency  interval. 

The  averages  given  in  table  24  are  obtained  from  the  data  of  table 
32,  which  contains  the  frequencies  of  all  the  fluorescence  bands  observed 
in  the  spectra  of  the  four  double  chlorides  when  excited  at  the  tempera- 


72 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


tiire  of  liquid  air.    As  in  the  corresponding  table  for  +20°  (table  30) 
the  arrangement  is  by  series. 

Table  24. — Average  intervals  of  the  fluorescence  series  at  -185^  C. 


Series. 

K. 

NH4. 

Kb. 

Cs. 

Average. 

Bi.... 
Ba.... 

B3.... 

Cx.... 

C2.... 

Di.... 
Di' .  .  . 

83.9 
83.1 
83.5 
84.9 
82.7 
83.1 

83.0 
83.2 

84.2 
83.6 

83.0 

83.4 

83.53 
83.33 

84.1 
82.7 
83.8 

84.0 
82.9 
83.6 

83.7 
82.8 
83.1 
84.5 
83.6 
83.6 
83.2 
83.5 

84.18 
82.78 
83.40 

D2.... 

D2'... 

84.1 

84.2 

84.0 

83.98 

E2'.... 
E2"... 

83.6 

82.5 
83.3 
83.1 

83.10 
83.40 
82.83 
83.50 

Ai.... 
A2 

83.3 

82.1 
83.6 

83.4 

83.58 

83.32 

83.50 

83.44 

THE  ABSORPTION  SPECTRA. 

A  glance  at  the  absorption  spectra  of  the  double  chlorides,  obtained 
by  viewing  through  a  spectroscope  the  light  transmitted  by  the 
crystals  at  room  temperature,  shows  the  same  higher  degree  of  resolu- 
tion that  characterizes  the  fluorescence  spectra  of  these  salts.  The 
salient  feature  is  a  series  of  strong,  rather  narrow  bands,  equally  spaced 
as  to  frequency,  like  the  broader  bands  of  the  other  uranyl  compounds. 
The  interval,  as  in  all  uranyl  absorption  spectra,  is  distinctly  smaller 
than  the  fluorescence  interval.  Between  these  are  several  series  of 
weaker  bands. 

The  complete  mapping  of  the  absorption  spectra  is  difficult.  It  can 
not  be  done  visually,  since  the  bands  extend  out  into  the  darkness  of 
the  ultra-violet.  Photography  adds  considerable  detail,  but  does  not 
greatly  extend  the  range  toward  the  shorter  wave-lengths  on  account 
of  the  rapidly  increasing  opacity.  In  the  brighter  regions  of  the 
spectrum,  on  the  other  hand,  more  can  be  seen  with  the  eye  than  can 
be  found  on  the  photographic  plate.  The  data  which  we  have  obtained 
and  which  are  presented  in  the  tables  at  the  end  of  this  chapter  have 
been  procured  by  supplementing  the  photographic  method,  wherever 
desirable,  by  visual  observations. 

A  great  variety  of  light-filters  and  combinations  of  Hght-filters  have 
been  employed  in  different  parts  of  the  spectrum,  wdth  widely  different 
exposures  for  the  strong  and  weak  bands.  The  thickness  of  the  trans- 
mitting layer  has  likewise  been  varied  as  far  as  the  available  material 
would  permit.  We  are  convinced,  however,  that  the  extreme  limits  of 
the  absorption,  in  both  directions,  have  not  as  yet  been  reached. 

By  using  crystals  of  unusual  thickness,  especially  prepared  for  this 
work  and  sometimes  by  mounting  several  crystals  one  behind  the 


INTIMATE   STRUCTURE   ON   COOLING. 


73 


other,  so  as  to  greatly  increase  the  depth  of  the  transmitting  substance, 
it  has  been  found  possible^  to  greatly  extend  the  absorption  spectrum 
toward  the  red. 

Since  the  crystals  are  of  a  greenish-yellow  color,  they  become  rapidly 
transparent  as  the  light  admitted  is  changed  from  blue  to  yellow;  hence 
the  use  of  increasingly  thicker  layers  to  bring  out  the  absorption  bands. 
To  a  certain  extent  the  crystal  acts  as  a  screen  to  absorb  the  blue  light 
which  would  cause  fluorescence;  nevertheless  it  was  found  necessary 
to  interpose  orange  or  yellow  screens  of  different  densities  to  eliminate 
fluorescence  in  a  region  where  ordinarily  it  is  at  a  maximum.  At  first 
colored  glasses  obtained  from  Dr.  H.  P.  Gage,  of  the  Coming  Glass 
Company,  were  used  as  filters;  later,  solutions  of  potassium  bichromate 
of  varying  concentration.  It  is  evident  that  the  screening  must  be 
constantly  changed  when  light  from  the  arc  is  used  as  a  background  for 
bands  of  increasingly  longer  wave-length.  It  was  thought  that  a  beam 
of  monochromatic  fight  could  be  used  as  a  background  and  thus 
obviate  exciting  the  crystal  to  fluorescence,  but  a  preliminary  study 
indicated  that  such  a  beani  of  dispersed  light  could  not  be  made  of 
sufficient  intensity  to  bring  out  the  dimmer  bands. 


\    I    I 


\  I  l.i.t.1 1 1  n  I 


•*9M      WAfl-LIMTN. 


u 


*-^ 


i   i  I 


T~r 


I  I  l.iiil  I  1  h!  ii'i  h-.  i!  !  ii 

1 1 1  I  I     •  I  j  I 


!       TTT 


J_J_L 


n 


h-f 


U^fI4 


4. 


I   '■   '  U    i'nh   I    11   i*.  1  ,'il'!  !|!    ', 


i     i 


nice 


Hoo 


lojoo 


Fig.  61. — Fluorescence  bands  are  indicated  by  lines  above  the  horizontal.  Old  absorption  bands 
are  indicated  by  dotted  bands  below  the  line ;  new  absorption  bands  by  solid  bands  below  the 
horizontal.  The  plot  shows  only  a  portion  of  the  complete  spectra  of  the  following  salts  at 
+30°  C:  (1)  potassium  uranyl  chloride;  (2)  ammonium  uranyl  chloride;  (3)  rubidium  uranyl 
chloride;  (4)  caesium  lu-anyl  chloride. 

In  figure  61  is  pictured  a  portion  of  the  fluorescence  and  absorption 
spectrum  of  each  of  the  double  chlorides  studied.  Fluorescence  bands 
are  designated  by  lines  above  the  horizontal  line.  The  older,  well- 
established  absorption  bands  are  designated  by  dotted  lines  below  the 
horizontal  and  the  new  bands  by  solid  fines  below  the  horizontal.  The 
relative  positions  of  the  fluorescence  and  absorption  bands  are  readily 
seen.    These  bands  appear  to  be  of  two  distinct  classes: 

1  Howes,  H.  L.,  Physical  Reviow  (2),  xi,  p.  66.     1918. 


74 


FLUORESCENCE    OF   THE    URANYL    SALTS. 


(1)  Most  of  them  at  +20°,  as  may  be  seen  from  the  diagram  and 
from  table  25,  in  which  they  are  Hsted  together  with  the  corresponding 
fluorescence,  are  reversals  of  fluorescence.  These  do  not  form  a  con- 
tinuation of  the  absorption  series  lying  farther  toward  the  violet,  nor 
can  they  be  grouped  in  series  having  the  absorption  interval  of  71=^. 
In  all  four  species  every  fluorescence  band  of  groups  5  and  6  has  its 

Table  25. — New  absorption  bands  at  +20"  C. 


Potassium  uranyl  chloride. 

Ammonium  uranyl  chloride. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence, 
series. 

Absorp- 
tion 
series. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

1802.1 

1801.4 

B 

1802.5 

1803.1 

B 

1820.2 

1819.3 

C 

1820.8 

1820.7 

C 

1836.5 

1837.6 

D 

1838.9 

1839.7 

D 

1846.0 
1855.3 

c 

1848.8 
1857.8 

c 

1855.3 

E 

1856.9 

E 

1865.0 
1869.4 

d 

1869.2 
1871.8 

d" 

1869.6 

A 

1871.8 

A 

1879.0 
1885.1 

e 

1886.5 
1906.2 

1886.8 
1904.6 

B 
C 



1884.7 

B 

1902.2 

1901.5 

C 

1924.2 

1923.2 

D 

1920.9 

1920.1 

D 

1942.3 

1940.5 

E 

1937.6 

1938.3 

E 

1957.4 

1956.3 

A 

1954.7 

1953.5 

A 

Rul 

)idium  urj 

myl  chlor 

ide. 

Caesium  uranyl  chloride. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

1740.0 

1741.6 

C 

1791.5 

1789.7 

A 

1778.7 

1777.8 

E 

1808.0 

1808.6 

B 

1789.5 

1789.4 

A 



1829.2 

1827.5 

C 

1806.1 

1806.1 

B 



1843.0 

1840.5 

D 

1823.2 
1834.9 
1841.6 

1822.8 

C 

' "  V  * " 

1846.4 
1861.2 
1873.0 

/? 

1859.1 
1873.1 

E 
A 

1841.5 

D 

1859.8 

1859.8 

E 

1890.7 

1891.1 

B 

1872.0 

1873.1 

A 

1911.1 

1910.4 

C 

1889.0 

1890.0 

B 

1923.8 

1923.6 

D 

1907.2 

1905.5 

C 



1944.4 

1942.7 

E 

1926.7 

1925.0 

D 

1957.8 

1955.7 

A 

1941.7? 

d 

1944.0 

1943.5 

E 

1952  0? 

e? 

1958.7 

1957.1 

A 

corresponding  absorption  band,  and  this  relation  extends  to  some  of 
the  bands  of  group  4.  Indeed,  the  suspicion  would  seem  warranted 
that  were  the  proper  experimental  conditions  attainable  throughout 
the  spectrum,  every  fluorescence  band  would  be  found  to  have  its 
related  absorption  band  and  to  be  reversible  in  the  sense  in  which  that 
term  is  defined  in  a  subsequent  paragraph. 


INTIMATE   STRUCTUKE   ON   COOLING. 


75 


(2)  The  remaining  bands  listed  in  table  25  are  not  reversals  of 
fluorescence.  They  belong  to  existent  absorption  series,  of  which  they 
are  the  members  of  greatest  wave-length  as  yet  observed. 

It  should  be  noted  that  special  precautions  were  taken  to  avoid 
bias.  They  were  not  sought  for  by  locating  the  fluorescence  bands  and 
looking  for  reversals,  but  found  under  conditions  of  illumination  which 

Table  26. — New  absorption  hands  at  —185°  C. 


Potassium  uranyl  chloride. 

Ammonium  uranyl  chloride. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

1941.7 
1947.6 
1954.7 
1960.4 
1965.8 
1972.4 
1977.5 
1984.9 
1989.3 
1998.0 
2008.8 

1940.0 

Ea' 

ei 

62' 

ai 

b2 

bi 

C2' 

dx 
d2 

1945.9 
1953.5 
1956.6 
1963.5 
1967.7 
1973.6 
1977.1 
1981.0 
1984.9 
1992.0 
1996.8 
2002.8 
2006.8 
2014.1 

1945.0 
1953.7 

E2" 
Ai 

d2" 

62" 

&2' 
b2 
62" 

1963.9 
1972.3 
1977.8 

Bi 
Ba 
Bs 

1968.7 

Bi 

1977.9 

B2 

1997.2 
2007.4 

Di 

D2 

1992.7 

C2 

dl' 
dl" 
d^' 

Rubidium  uranyl  chloride. 

Caesium  uranyl  chloride. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absorp- 
tion 
series. 

Absorp- 
tion. 

Fluores- 
cence. 

Fluores- 
cence 
series. 

Absori)- 

tion 

series. 

1944.4 
1952.4 
1954.7 
1958.1 
1963.9 
1973.9 
1981.0 
1985.7 
1995.6 
2005.2 
2010.1 
2016.1 

dt" 

ei' 

1953.9 
1956.6 
1958.9 
1967.0 
1970.8 
1974.3 
1978.2 
1982.9 
1987.7 
1991.3 
1997.6 
2005.6 
2009.6 
2016.1 
2022.2 

d2" 

62' 

ax' 

1957.9 

Ai 

62' 

ai' 
61" 

&2 

61' 
61" 
62' 

&2" 

61 

Cl 
C2 

dx 
d^' 
da" 

C2 

di 
d^' 
d2" 

2003.7 

Di 

1997.6 

Ci 

2008.5 
2014.9 

D2' 

rigorously  excluded  fluorescence,  and  in  many  instances  their  existence 
and  place  was  checked  by  two  observers  working  independently. 

The  fact  that  practically  the  entu-e  group  was  in  approximate  coin- 
cidence with  fluorescence  was  an  unlooked  for  result  of  which  we  became 
aware  only  after  the  measurements  had  subsequently  been  plotted. 
The  expectation  was  that  these  bands  would  prove  to  be  members  of 
the  absorption  series  lying  farther  toward  the  violet. 


76 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


A  search  by  similar  methods  failed  to  reveal  any  bands  of  class  (1), 
mentioned  above,  in  the  spectra  of  the  crystals  when  cooled  to  the 
temperature  of  liquid  air.  No  selective  absorption  could  be  detected 
beyond  the  violet  end  of  group  6,  l/\  1940,  and  while  a  considerable 
number  of  new  absorption  bands  were  detected,  nearly  all  of  these 
(see  table  26)  were  found  to  be  members  of  series  already  recognized. 
The  exceptions,  two  each  in  the  spectra  of  the  ammonium,  rubidium, 
and  caesium  double  chlorides,  do  not  appear  to  be  related  to  the  fluores- 
cence. Coincidences  between  fluorescence  and  absorption  are  of  the 
sort  already  established  as  characteristic  of  the  reversing  region. 

Table  27. — Average  intervals  of  absorption  series  at  -\-20^  C. 


Series. 

K. 

NH4. 

Rb. 

Cs. 

Av. 

b 

70.5 

71.6 

70.4 

70.9 
70.6 

70.9 
70.3 

70.9 

70.0 
70.5 

'7o!9' 
70.5 

70.3 
70.3 

'69^7 

13 

c 

70.8 
70.4 

68.8 
70.7 

70.3 
70.4 

7 

d' 

d 

d" 

c     ... 

71.1 
70.6 

70.0 
70.4 

71.0 
70.3 

69.7 
70.8 

71.2 

70.8 
69.6 

70.6 
70.8 

c" 

a" 

Av. . .  . 

70.0 

69.3 

70.5 

70.4 

70.3 

70.6 

The  failure  to  find  the  bands  in  groups  5  and  6  is  not  surprising. 
They  are  sufficiently  difficult  objects  at  +20°,  where  two  or  more 
components  are  blended  into  a  broader  band.  The  existence  of  these 
components  at  —185°  may  be  regarded  as  probable,  but  they  were 
invisible  under  the  conditions  which  we  have  thus  far  been  able  to 
obtain. 

The  absorption  spectra  of  the  double  chlorides  do  not  exhibit  the 
same  remarkable  approach  to  identity  of  structure  and  regularity  of 
arrangement  manifested  in  the  fluorescence  spectra.  Upon  analysis, 
however,  they  are  all  found  to  consist  of  series  having  intervals  of 
approximately  70  frequency  units.  As  may  be  seen  from  table  27, 
this  interval  for  a  given  series  is  very  nearly  the  same  for  all  four  salts. 
The  average  interval  for  all  the  series  of  a  given  salt  is  constant  within 
the  errors  of  observation.  These  averages  are  based  on  the  values  in 
table  33  at  the  end  of  this  chapter. 

The  absorption  bands,  unlike  those  of  the  fluorescence  spectrum,  do 
not  appear  to  fall  into  a  succession  of  strictly  homologous  groups,  but 
this  is  because  some  series  disappear,  while  others  increase  in  strength 


INTIMATE   STRUCTURE   ON   COOLING. 


77 


toward  the  violet.  A  group  near  the  fluorescence  region,  therefore, 
differs  notably  in  aspect  from  one  in  the  extreme  violet,  and  it  is 
difficult  to  base  conclusions  on  the  location  of  the  centers  of  the  groups, 
as  was  done  in  the  study  of  the  fluorescence  spectra. 

As  may  be  observed  in  figure  62,  where  the  ninth  group  for  the  four 
spectra  at  +20°  is  plotted,  the  distances  between  the  consecutive 
bands  are  less  nearly  equal  than  the  distances  between  fluorescence 
bands.  It  is  also  evident  from  this  figure  that  with  increasing  molecular 
weight  there  is  a  general  shift  toward  the  violet.  The  shift  is  apparently 
less  systematic  than  with  the  fluorescence  bands  and  several  reverse 
shifts  seem  to  occur.  In  general,  however,  the  total  displacement  is 
approximately  the  same  as  that  observed  for  fluorescence,  i.  e.,  5 
frequency  units  from  potassium  to  caesium. 

EFFECT  OF  TEMPERATURE  ON  THE  ABSORPTION  SPECTRA. 

In  the  study  of  the  absorption  of  the  double  chlorides  at  — 185°,  a 
modification  of  the  method  described  in  a  previous  paragraph  in 
the  investigation  of  the  fluorescence  at  low  temperatures  was  made. 
(See  fig.  56.)  The  crystal  under  observation  was  mounted  within  a 
Dewar  flask  and  submerged  in  liquid  air.  Light  was  transmitted 
through  the  crystal  instead  of  being  reflected  from  its  surface  and  a 
nitrogen-filled  tungsten  lamp  was,  in  general,  substituted  for  the 
carbon  arc.  Both  photographic  and  visual 
methods  were  tried,  and  in  the  reversing 
region,  especially,  where  fluorescence  and 
absorption  overlap,  much  attention  was 
given  to  the  selection  of  color-screens  to 
exclude  fluorescence  from  the  portion 
under  consideration, 

A  complete  list  of  the  absorption  bands 
observed  at  — 185°  will  be  found  in  table  34. 

The  three  most  obvious  results  of  cool- 
ing to  the  temperature  of  liquid  air  are : 
(1)  a  general  shift  toward  the  violet;  (2)  a 
great  increase  in  the  number  of  bands;  (3) 
a  very  decided  narrowing  and  sharpening 
of  the  bands. 

These  changes  are  readily  accounted  for 
by  the  assumption  already  made,  in  this 
chapter,  that  the  bands  at  +20°  Care  con- 
cealed doublets  and  that  the  effect  of  cool- 
ing is  to  resolve  them  while  simultaneously 
reducing  the  strength  of  the  stronger  and  increasing  the  strength  of  the 
weaker  component.  The  apparent  shift  thus  produced  will  vary  from 
zero  to  5  or  more  units,  according  to  the  distance  between  the  com- 
ponents. 


Fig.  62. 


78  FLUORESCENCE    OF  THE   URANYL   SALTS. 

A  few  bands  at  —185°  are  so  located  with  regard  to  the  +20°  bands 
that  to  explain  them  by  this  theory  we  must  suppose  them  to  be  too 
feeble  at  +20°  for  detection  and  greatly  increased  in  intensity  by 
cooling. 

There  is  also  evidence  in  places  of  further  resolution  into  closer 
narrow  doublets  and  as  the  degree  of  resolution  is  not  always  the  same 
with  fluorescence  and  the  corresponding  absorption,  this  is  a  source  of 
trouble  in  the  attempt  to  find  the  fluorescence  series  which  belongs  to 
each  series  in  the  absorption  spectrum.  Every  low-temperature  band, 
however,  falls  into  a  series  of  constant  frequency,  whatever  its  position 
or  degree  of  resolution. 

The  effect  of  temperature  on  the  average  intervals  can  be  studied  by 
comparing  tables  27  and  28.  Although  the  intervals  range  from  69  to 
71,  there  is  little  that  can  be  termed  systematic  in  the  variations. 

At  liquid  air  temperature,  where  two  or  more  components  are  present, 
we  have  used  subscripts.  Thus  di,  corresponds  to  Di,  c?2  to  D2,  etc. 
Where  the  reversal  is  doubled  in  the  manner  shown  in  figure  63,  we 
have  designated  this  doublet  as  di  and  d/',  etc. 

The  average  interval  of  each  salt  is  approximately  the  same  at 
both  temperatures.  It  will  be  noticed  in  table  27  that  70.28,  the 
average  of  the  c  components  is  smaller  than  the  h,  d,  e,  or  a 
averages.  This  is  of  interest  because  the  strong  C  series,  which 
join  these  series,  are  also  the  shortest  of  the  fluorescence  series.  Since 
the  —185°  bands  are  very  sharp  and  easy  to  locate,  no  doubt  the 
differences  found  in  table  28  are  indicative  of  real 
variations  in  the  constant-frequency  intervals.  It 
does  not  follow  that  the  smaller  intervals  are  con- 
fined to  one  salt  or  one  set  of  bands,  however,  since,  as 
has  been  noted  in  the  case  of  series  Ci  and  C2  of  the 
fluorescence  series,  the  maximum  difference  in  interval 
may  be  associated  with  two  series  which  are  nearly  co- 
incident. The  comparison  of  table  27  with  table  28 
shows  that  the  effect  of  changing  temperature  on  the  ^°"  ^^' 

average  interval  of  a  salt  is  almost  negligible,  but  that  the  two  com- 
ponents of  one  series  of  the  +20°  spectrum  may  vary  by  as  much  as 
1.9  units  in  frequency  interval. 

The  character  of  the  change  in  the  absorption  spectra  when  we  pass 
from  +20°  to  —185°  can  best  be  seen  in  detail  by  plotting  a  single 
group  in  the  spectrum  of  each  salt,  as  has  been  done  for  group  9  in 
figure  62.  A  better  idea  of  the  phenomena  of  cooling,  as  a  whole,  is 
obtained  by  means  of  maps  like  those  in  figures  64,  65,  66,  and  67,  in 
which  all  the  bands  of  fluorescence  and  absorption  are  given  at  both 
temperatures,  first  in  a  single  line  as  they  occur  in  the  spectrum  of  each 
salt.  Fluorescence  is  indicated  by  vertical  lines  above  the  horizontal 
and  absorption  below.    Length  of  line  indicates  roughly  the  strength 


D 

d,' 

£," 

1 

INTIMATE   STRUCTURE   ON   COOLING. 


79 


of  the  bands.  No  attempt  has  been  made  to  denote  the  width  of  the 
bands.  Below  each  spectrum  the  absorption  bands  are  sorted  out  into 
their  respective  series.  The  figure  is  necessarily  on  a  greatly  reduced 
scale.  Our  working  maps  of  these  spectra  are  about  2  meters  in  width. 
From  these  maps  some  of  the  statements  already  made  can  be 
verified  at  a  glance;  e.  g.,  the  increased  number  of  bands  and  series 
at  —  ISS"";  the  greater  extent  of  absorption  toward  the  red  at  +20° 
than  at  —185°,  and  that  there  is  in  general  a  greater  degree  of  resolu- 
tion of  absorption  than  of  fluorescence.  It  may  also  be  noted  that  the 
known  absorption  spectrum  is  of  greater  extent  than  the  fluorescence 
spectrum  and  that  the  absorption,  considered  as  a  unit,  suffers  a  nar- 
rowing on  cooling  which  is  more  marked  on  the  side  toward  the  red. 

Table  28. — Average  intervals  of  absorption  series  at  —185°  C. 


W. 
bi. 
W 
W. 
62. 
W 


K. 


70.6 


70.5 


69.3 
70.0 
69.0 


69.8 


70.0 
70.2 


NH4. 


71.4 


71.0 


71.4 
71.2 


70.9 


70.8 


70.5 


Kb. 


71.3 


70.7 


70.7 


70.4 
70.9 


70.9 


71.2 
7l!l 


Cs.      Average. 


70.4 


70.6 
70.2 


70.7 


70.3 
70.5 
70.9 


70.2 
70.5 
71.0 
70.7 


70.50 
71.40 
71.30 
70.80 
70.47 
71.40 
70.95 


70.83 


70.30 
70.60 
70.10 
70.43 
69.95 


70.28 


70.35 
70.50 
70.85 
70.50 
70.68 
70.20 


70.51 


Series. 


a    av. 
Av... 


K.       NH4.      Rb. 


70.6 
70.5 


70.0 
70.4 
71.9 


70.22 


70.7 


71.4 


71.3 


71.06 


70.7 
70.9 


70.8 


71.0 


70.4 


70.84 


Cs. 


70.0 
70.3 
70.8 


71.0 


70.6 


70.54 


Average. 


70.70 
70.73 
70.25 
70.55 
71.10 


70.67 


71.00 
70.65 
70.47 
71.90 


71.00 


REVERSALS  AND  THE  REVERSING  REGION. 

The  phenomena  of  the  reversing  region,  where  fluorescence  and 
absorption  overlap,  are  complicated.  Some  points  applicable  particu- 
larly to  the  double  chlorides  are,  however,  discussed  here. 

The  early  observers  of  uranyl  spectra  were  of  the  opinion  that  some 
connection  or  relation  must  exist  between  the  system  of  bands  of 
fluorescence  and  absorption.  Becquerel  and  Onnes,  who  first  studied 
these  spectra  at  low  temperatures,  were  able  to  confirm  the  impression 
of  Stokes  that  the  two  systems  overlapped  and  that  there  was  actual 


80 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


coincidence  of  position  between  certain  fluorescence  bands  and  absorp- 
tion bands. 

In  the  case  of  the  double  chlorides  at  +20°,  each  series  of  bands  of 
the  fluorescence  system  comes  into  coincidence,  or  near  coincidence, 
with  an  absorption  band  in  what  we  have  termed  the  reversing  region, 
which  is  approximately  that  region  occupied  by  group  7  of  the  fluores- 
cence spectrum. 

The  fact  that  the  reversal  sometimes  appears  to  be  exact,  within  the 
errors  of  observation,  while  sometimes  there  is  a  displacement  of  several 
units  of  frequency,  might  seem  to  render  such  a  general  relation  doubt- 
ful, but  the  discrepancy  can  be  shown  to  be  a  necessary  consequence  of 
the  fact  that  both  fluorescence  and  absorption  bands  at  this  tempera- 
ture are  unresolved  complexes.    The  true  nature  of  the  case  may  be 


+20- 


ill 


III!  I  1. 1  I  I  I 


^ 


'''^■^'"'^Mlriii"'ii'i '  "'1'^  "'  ■  II 'I  I'll  II' 


\i     II     II      I 


III      I 


II       I       III            III       I       in    r 
n \ tH 7~r — ri — I 1 — 


-185 


ii'i"|ii""'H"|  i"i"'i"iTi'ii'i'|'   |'i"~m[r 


III  I  II     I     I  :    I 

~Ti      II       r     I 


i:ii     II     III    ill     II      II   I  II  I  ; 

II    I  I       I       ill!      nil fi — rr 


"I r 


¥ 


+20°  I 


I  I  ■  I  ll 


rH4- 


NH4 


''||"lll'l"l||l  "  M"  |'l|  I  '    I  I    ll'jll  I  II 


I  !    I'     I       III       I  — r 
T 1I — n — Ti — r 


T-r-T 


II       I      III      I      r 
I  '      '      "  I  ' 


I       n     I       I      r 


-185 


JJLL 


ill.    Mil 


"■■«■  '■l''iy.l'JiU 


ii"i|'"|i""''iiirin'Ti'"|ii|'ii'i'||'"||r'|  'Tf 


in  I    nil — n — rrt — 11     11 — itn — ri — n — rr 


Ti — fT 


~iTr- 
II  I  II 


TV 


I        M 


I      TI 


II 
T-TT 
_2Slfifi. 


II    I   n       I 
III    II — rr 


Jft 


00 


jfifiS. 


jsm. 


seen  from  figure  68,  which  is  from  a  sketch  of  such  a  reversal  at  — 185°, 
where  the  resolution  is  more  nearly  complete.  Here  the  fluorescence 
and  absorption  are  complementary,  the  strong  components  of  fluores- 
cence coinciding  with  the  weak  absorption  component  and  vice  versa. 
When  the  resolution  is  less  complete,  the  weaker  components  will  dis- 
appear, and  although  the  reversal  for  each  component  is  exact,  there 
will  be  an  apparent  failure  to  reverse,  or,  in  other  words,  we  see  the 
strong  components  displaced. 

An  actual  instance  in  which  this  relation  between  fluorescence 
appears  is  given  in  plate  1,  a,  which  is  from  a  photograph  of  a  small 
portion  of  the  reversing  region.  The  upper  half  contains  the  com- 
ponents of  a  resolved  fluorescence  band,  the  lower  half  the  correspond- 


INTIMATE   STRUCTURE   ON   COOLING. 


81 


ing  components  of  the  absorption  band  with  fluorescence  ehminated. 
In  this  photograph  each  component  of  the  fluorescence  has  its  exact 
reversal  in  absorption,  with  reciprocal  relations  as  to  intensity  indi- 
cated in  figure  68.  The  weaker  component  of  fluorescence  is  coin- 
cident with  the  stronger  component  of  the  absorption  doublet,  and 
vice  versa. 

In  the  reversing  region  fluorescence  and  absorption  are  mutually 
destructive.  Consequently  one  or  both  are  sometimes  invisible;  but 
knowing  the  intervals,  we  can  locate  the  reversal.  By  proper  screening 
the  fluorescence  may  be  prevented  and  the  absorption  band  brought 
Out;  and  by  taking  extra  precautions  to  secure  a  dark  background  and 
to  increase  the  excitation  the  fluorescence  may  be  seen.  Thus  the  com- 
putation may  be  confirmed. 


+20 


ill 


'"l""l'lilll,llilluil||l,||j| 


II  I  III 


MITII   I  " 


I  I    I      I      III 
-T — I — h — I 


I     III      I      III      I — r 
"1 — n — i — I      II — I — 


1 — I n — r 


I      I     n 


-185 


lM 


■  Jli^|WJf||»||i[|.m|im|n|||.   I'  |j|»M»|W| 


fi   |r""|li 


I!  I  II  II        III        I     ~T~ 

~1 — n — I — n — I rr 


i\ — n r 


rrn — rr 


I      II     II     II    III      r 

-|        [-n n rr-4— m 1 


I       r 


I    ,    I 1 r 


I       r 


+20 


■"  '""'"\llUilllh 


c^ 


iMi  in  i<  r 


'I" I"  1 1 


II      11        II        II       T 


I      I      I      n       r 


X — r 


1 — n 1 — r 


T      I      n  r 


I       t       I    :    I       I 


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ll     iJli  ji't"'''-'i'^-ii[||||^|,|.y,|,,pJ^ 


inT-TTTrw]W 


nin 


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T^^T^ 


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III       HI 


n        n       II 


T— + 


16100 


jsm. 


TTn — I — n — I — I      n — 

20100        22J20 I UiSSL 


?W9 


In  the  study  of  the  double  chlorides  the  matter  is  further  confused 
because  the  difference  between  the  fluorescence  interval  (83+)  and 
that  of  the  absorption  interval  (70+)  is  approximately  equal  to  the 
distance  between  neighboring  bands  in  the  fluorescence  groups.  An 
absorption  series  which  comes  into  coincidence  with  band  C,  groupi  7, 
will  therefore  nearly  coincide  with  band  B,  group  8,  etc.  Furthermore, 
I  the  degree  of  resolution  in  the  absorption  spectrum,  as  has  already  been 
mentioned,  is  often  greater  than  in  the  fluorescence  spectrum,  and 
certain  series  are  observable  of  which  the  corresponding  fluorescence 
bands  can  not  be  identified. 


82 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


So  far  as  the  spectra  at  +20°  are  concerned,  we  find  that: 

(1)  All  absorption  bands  toward  the  violet  from  the  reversing  region 
occur  in  series  with  constant-frequency  intervals. 

(2)  For  every  fluorescence  series  there  is  a  corresponding  absorption 
series. 

Whether  the  relation  between  absorption  and  fluorescence  outlined 
above  is  significant  can  best  be  determined  by  the  study  of  the  spectra 
for  -185°. 

If,  for  example,  the  explanation  of  the  numerous  instances  of  inexact 
coincidence  is  valid,  we  should  expect  exact  reversals  of  the  components; 
also  that  the  components  of  the  resolved  absorption  spectra  form  series 
definitely  related  to  the  components  of  the  fluorescence  spectra  in  a 
manner  consistent  with  the  system  indicated  for  the  spectra  at  -|-20°. 
From  a  study  of  the  exactness  of  the  reversals  in  the  resolved  spectra  at 
low  temperatures  it  appears  that  25  out  of  38  fluorescence  series  are 
certainly  reversed  and  that  36  fluorescence  series  join  absorption  series 
in  the  seventh  group.  The  experimental  error  in  this  group  does  not 
exceed  1.5  units.    The  difference  in  position  between  fluorescence  and 

absorption  is  sometimes  greater  than  1.5,  but  this  may 

be  ascribed  to  the  dissymmetry  in  the  form  of  the  bands. 

Fluorescence  bands  have  their  crest  toward  the  violet, 
absorption  bands  toward  the  red.  In  the  case  of  reversals, 
these  regions  tend  to  annul  each  other,  leaving  a  rem- 
nant of  fluorescence  on  the  red  side  and  a  remnant  of 
absorption  on  the  violet.  The  result  is  that  in  regions 
where  fluorescence  and  absorption  exist  together,  fluo- 
rescence bands  are  apt  to  be  given  too  great  a  wave- 
length, and  vice  versa.  In  the  C2  series  of  the  rubidium 
chloride,  for  example,  there  is  a  displacement  of  2.6  units 
between  the  observed  positions  of  fluorescence  and 
absorption. 

If,  however,  we  compute  the  proper  positions  of  these  bands,  using 
the  average  intervals  for  the  C2  and  C2  series  respectively,  thus  elimi- 
nating the  displacements  in  the  reversal  region,  the  fluorescence  band 
and  absorption  thus  established  agree  in  position  within  0.3  unit. 
The  impossibility  of  excluding  all  absorption  when  fluorescence  is 
present,  and  the  impossibility  of  preventing  a  tendency  toward 
fluorescence  when  absorption  alone  is  sought  for  may  well  account 
for  the  resulting  displacement.  The  case  of  the  C2  series  is  not  an 
isolated  one — probably  every  reversal  is  affected  somewhat  and  the 
stronger  bands  the  most;  there  being  always  an  apparent  shift  of  the 
absorption  band  toward  the  violet  and  of  the  fluorescence  band 
toward  the  red.  This  phenomenon  has  long  been  recognized  by  the 
authors  in  connection  with  broad  fluorescence  bands,  and  it  must  now 
be  recognized  in  the  reversing  of  the  narrow,  line-like  bands  at  the 
temperature  of  liquid  air. 


FL. 

ABS. 

Fig.  68. 


INTIMATE    STRUCTURE    ON    COOLING.  83 

In  the  above,  the  reversals  which  connect  fluorescence  to  absorption 
series  have  been  sought  for  in  the  seventh  group.  There  are,  however, 
other  possible  connections,  for  coincidences  occur  in  the  sixth  and 
eighth  groups  as  well.  Since,  as  has  already  been  pointed  out,  the 
difference  in  spacing  between  a  fluorescence  and  absorption  interval 
is  nearly  the  same  as  the  spacing  between  fluorescence  bands,  it  is  often 


T»R6  20I60  '  2iToo iToT 

POTASSIUM     URANYL   CHLORIDE 


AMMONIUM     URANYL  CHLORIDE 

J L 


rr         n  n  rr 


oJL 


Al 


RUBIDIUM      URANYL    CHLORIDE 
J I 


hJL 


M 


n     :      n  rr 


CAESIUM     URANYL    CHLORIDE 
—J I 


±1 


1 1  r 

T \  r 


^ 


jki 


1  r 

"1  r 


AL 


Fig.  69. 

possible  to  join  equally  well  two  fluorescence  series  to  one  absorption 
series,  a  fact  which  makes  it  difficult  to  determine  the  true  relation  in 
the  case  of  this  class  of  salts. 

The  actual  manner  in  which  the  reversals  between  fluorescence  and 
absorption  occur  is  shown  in  figure  69,  which  is  a  diagram  of  the  revers- 
ing region.    Here  the  plotting  is  quite  accurate,  the  fluorescence  bands 
above  and  the  absorption  bands  below  the  horizontal.    Dotted  lines 
ndicate  computed  positions.    This  figure  is  approximately  10  times  as 


84 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


large  as  the  original  negatives.  To  avoid  confusion,  the  various  series 
occurring  in  each  salt  are  vertically  displaced  instead  of  being  drawn 
on  a  single  line,  as  they  appear  in  the  actual  spectra.  An  inspection 
of  this  diagram  will  suffice  to  indicate  the  approach  to  complete  coin- 
cidence in  the  reversals  and  the  type  of  departure  from  coincidence. 

Table  29. — General  list  of  fluorescence  hands  in  spectra  of  the  double  uranyl  chlorides 

at  +20"  C. 


Potassium 

Ammonium 

Rubidium 

Caesium 

Group 
and 

uranyl  chloride. 

uranyl  chloride. 

uranyl  chloride. 

uranyl  chloride. 

series. 

X 

ixiO^ 

A 

X 

-XIO' 

A 

X 

^X103 
X 

X 

ixiO* 

A 

1 

C 
D 
E 
A 

B 

0.6809 
.6716 
.6635 
.6571 
.6501 

.6430 

1469.7 
1489.9 
1507.1 
1521.8 
1538.2 

1655.3 

0.6436 

1553.7 

0.6420 

1657.6 

0.6401 

1662.3 

C 

.6375 

1568.6 

.6358 

1572.6 

.6354 

1573.8 

.6336 

1578.3 

2 

D 

.6303 

1586.6 

.6291 

1589.6 

.6281 

1592.2 

.6289 

1590.1 

E 

.6225 

1606.4 

.6231 

1604.9 

.6206 

1611.3 

.6219 

1608.0 

A 

.6171 

1620.5 

.6172 

1620.2 

.6162 

1622.8 

.6156 

1624.4 

fB 

.6111 

1636.5 

.6103 

1638.6 

.6098 

1640.0 

.6090 

1642.0 

C 

.6051 

1652.5 

.6041 

1655.3 

.6030 

1658.3 

.6016 

1662.5 

3 

D 

.5983 

1671.5 

.6978 

1672.7 

.5967 

1675.9 

.5970 

1675.0 

E 

.5919 

1689.5 

.5923 

1688.2 

.6903 

1694.1 

.5911 

1691.9 

A 

.5869 

1704.0 

.5866 

1704.8 

.5860 

1706.4 

.6854 

1708.2 

B 

.6816 

1719.4 

.5813 

1720.3 

.5800 

1724.0 

.5789 

1727.4 

C 

.5759 

1736.4 

.5752 

1738.6 

.6742 

1741.6 

.5729 

1745.4 

4 

D 

.5698 

1754.9 

.6696 

1755.7 

.5686 

1758.7 

.5689 

1757.9 

E 

.5642 

1772.3 

.5642 

1772.3 

.5625 

1777.8 

.6631 

1775.9 

A 

.5595 

1787.2 

.5593 

1787.9 

.6588 

1789.4 

.5587 

1789.7 

fB 

.5551 

1801.4 

.5546 

1803.1 

.6637 

1806.1 

.5629 

1808.6 

C 

.5497 

1819.3 

.5492 

1820.7 

.5486 

1822.8 

.5472 

1827.6 

5 

D 

.5442 

1837.6 

.5436 

1839.7 

.5430 

1841.5 

.5433 

1840.6 

E 

.5390 

1855.3 

.5385 

1856.9 

.6377 

1859.8 

.5379 

1859 . 1 

A 

.5349 

1869.6 

.5342 

1871.8 

.5339 

1873.1 

.6339 

1873.1 

fB 

.5306 

1884.7 

.6300 

1886.8 

.6291 

1890.0 

.5288 

1891.1 

C 

.5259 

1901.5 

.5250 

1904.6 

.5248 

1905.5 

.6234 

1910.4 

6 

D 

.5208 

1920.1 

.5200 

1923.2 

.5195 

1925.0 

.5198 

1923.6 

E 

.5159 

1938.3 

.5153 

1940.5 

.5145 

1943.5 

.5147 

1942.7 

A 

.5119 

1953.5 

.5112 

1956.3 

.5110 

1957.1 

.6113 

1965.7 

B 

.5078 

1969.4 

.5072 

1971.5 

.5066 

1973.8 

.5067 

1973.6 

C 

.5039 

1984.4 

.5031 

1987.6 

.5027 

1989.1 

.6024 

1990.3 

7 

D 

.4990 

2004.0 

.4986 

2005.7 

.4979 

2008.4 

.4989 

2004.4 

E 

.4946 

2021.7 

.4940 

2024.1 

.4935 

2026.2 

.4937 

2025.6 

A 

.4909 

2036.9 

.4904 

2039.2 

.4899 

2041.4 

.4904 

2039.2 

fB 

.4869 

2053.8 

.4867 

2054.6 

.4857 

2069.0 

.4863 

2056.3 

C 

.4836 

2068.0 

.4829 

2071.0 

.4824 

2072,8 

.4819 

2076.0 

8 

D 
E 
A 







^ 

INTIMATE   STRUCTURE   ON   COOLING, 


85 


With  regard  to  the  reversing  region  at  - 185°,  it  can  be  stated  that— 

(1)  The  majority  of  the  fluorescence  series  reverse  in  the  seventh 
group. 

(2)  36  out  of  38  fluorescence  series  are  joined  in  the  seventh  group 
to  absorption  series. 

(3)  The  exactness  of  reversal  depends  not  only  on  the  structure  of 
the  band,  but  on  the  simultaneous  presence  of  fluorescence  and  absorp- 
tion in  this  region. 

(4)  Other  reversals  and  connections  are  present  in  the  groups  adja- 
cent to  group  7. 

Table  30. — Frequencies  and  intervals  of  fluorescence  series  at  +20°  C. 


Group 
1. 


Group 
2. 


Group 
3. 


Group 
4. 


Group 
5. 


Group 
6. 


Group 
7. 


Group 

8. 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals  (observed) 


1636.5  1719.4  1801.4  1884.7 

1635.5  1718.9  1802.3  1885.7 

-1.0    -0.5    +0.9    +1.0 

82.9      82.0     83.3      84 


1969.4 

1969.1 

-0.3 


2053.8 

2052.6 

-1 


84.4 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals  (observed) 


1469.7  1555.3  1638.6  1720.3  1803.1  1886.8 

1470.9  1554.3  1637.6  1720.9  1804.3  1887.6 

+1.2    -1.0    -1.0    +0.6    +1.2    +0.8 

85.6       83.3     81.7     82.8     83.7     84 


Kb 


Cs 


{Frequencies  (observed) . 
Frequencies  (calculated . 
Differences 
Intervals  (observed) 


{Frequencies  (observed) .  , 
Frequencies  (calculated) 
Differences 
Intervals  (observed) 


1557.6 

1556.2 

-1.4 


1640.0 

1639.7 

-0.3 


1724.0 

1723.2 

-0.8 


1806.1 

1806.7 

+0.6 


1890.0 

1890.1 

+0.1 


1971.5 

1970.9 

-0.6 

7      83 

1973.8 

1973.6 

-0.2 


2054.6 

2054.3 

-0.3 

.1 

2059.0 

2057.1 

-1.9 


83.4     84.0      82.1      83.9      83.8     85.2 


1562.3 

1562.0 

-0.3 


1727.4 
1726.6 
-0.8 
81.6      83.5       81 


1643.9 

1644.3 

+0.4 


1808.6 

1809.0 

+0.4 


1891 . 1 

1891.3 

+0.2 


1973.5 

1973.6 

+0.1 


2056.3 

2055.9 

-0.4 


2    82.5      82.4     82.8 


Series  C. 


K 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


Cs 


fFrequencies  (observed) . 
J  Frequencies  (calculated) 

I  Differences 

Ilntervals 


1489.9 

1489.4 

-0.5 


1568.6 

1569.3 

+0.7 


1652.5 

1652.4 

-0.1 


1736.4 

1735.6 

-0.8 


1819.3 

1818.7 
-0.6 


1901.5 

1901.8 

+0.3 


1984.4 

1984.9 

+0.5 


2068.0 

2068.0 

0.0 


83.9      83.9     82.9      82.2      82.9      83.6 


1572.9 

1572.4 

-0.5 


1655.3 

1655.4 

+0.1 


83.0      82.4 


1738.6 

1738.4 

-0.2 

3      82 


1820.7 

1821.4 

+0.7 


1904.6 

1904.4 

-0.2 


1987.6 

1987.4 

-0.2 


1      83.9      83.0 


1573.8 

1574.5 

+0.7 

84 

1578.5 

1579.6 

+1.1 


1658.3 

1657.5 

-0.8 


1822.8 
1823.4 
+0.6 
83.3      81.2     82 


1741.6 

1740.4 

-1.2 


1905.5 

1906.4 

+0.9 

7      83 


1989.1 
1989.3 
+0.2 
6     83.7 


2071.0 
2070.4 

-0 
,4 

2072.8 

2072.3 

-0.5 


1662.5 

1662.1 

-0.4 


1745.4 

1744.6 

-0.8 


1827.6 

1827.1 

-0.4 


1910.4 

1909.6 

-0.8 


1990.3 
1992.0 

+1.7 


2075.0 

2074.6 

-0.4 


84.0     82.9      82.1      82.9     79.9     84.7 


86 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  30. — Frequencies  and  intervals  of  fluorescence  series  at  +20°  C — continued. 

Series  D. 


Group 
1. 


Group 
2. 


Group 
3. 


Group 
4. 


Group 
5. 


Group 
6. 


Group 

7. 


Group 

8. 


K 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


1586.6 

1587.6 

+1.0 


1754.9 
1754.2 
-0.7 
84.9      83.4      82 


1671.5 

1670.9 

-0.6 


1837.6 

1837.5 

-0.1 


1920.1 

1920.8 

+0.7 


2004.0 

2004.1 

+0.1 


82.5      83.9 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


1507.1 

1506.6 

-0.5 

82 


Rb 


Cs 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


1589.6 

1589.8 

+0.2 

5      83 

1592.2 

1592.4 

+0.2 


1672.7 

1755.7 

1839.7 

1923.2 

1673.0 

1756.2 

1839.4 

1922.6 

+0.3 

+0.5 

-0.3 

-0.6 

2005.7 

2005.8 

+0.1 


1      83.0      84.0      83.5      82.5 


1675.9 

1758.7 

1841.5 

1925.0 

1675 . 6 

1758.7 

1841.9 

1925 . 1 

-0.3 

0.0 

+0.4 

+0.1 

2008.4 
2008.2 
0.2 


83.7      82.8      82.8      83.5      83.4 


1590.1 

1592.2 

+1.1 


1675.0 

1757.9 

1840.5 

1923.6 

1675.0 

1757.9 

1840.7 

1923.6 

0.0 

0.0 

+0.2 

0.0 

2004.4 

2006.4 

+2.0 


84.9      82.9      82.6 


80.8 


Series  E. 


1  Frequencies  (observed) . . 
Frequencies  (calculated) 
Differences 
Intervals 


(Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


Ca 


ITFrequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


1521.8 

1521.2 

-0.6 

83 


1689.5 

1772.3 

1855.3 

1938.3 

1689.4 

1772.4 

1855.4 

1938.4 

-0.1 

+0.1 

+0.1 

+0.1 

82.8     83.0      83.0     83 


1606.4 

1606.4 

0.0 

83 

1604.9 
1605.0 
+0.1 
1      83.3      84.1      84.6      83.6 


1611.3 

1611.4 

+0.1 

82.8      83.7      82.0      83.7      82 


1688.2 

1772.3 

1856.9 

1940.5 

1688.8 

1772.6 

1856.4 

1940.2 

+0.6 

+0.3 

-0.5 

-0.3 

1694.1 

1777.8 

1859.8 

1943.5 

1694.1 

1777.3 

1860.3 

1943.3 

0.0 

-0.5 

+0.5 

-0.2 

1608.0 

1608.4 

+0.4 


1691.9 

1775.9 

1859.1 

1942.7 

1691.9 

1775.4 

1858.9 

1942.3 

0.0 

-0.5 

-0.2 

-0.4 

83.9      84.0      83.2      83.6      82 


2021.7 
2021.4 
-0.3 
.4 

2024.1 
2024.0 
-0.1 
.6 

2026.2 
2026.2 
0.0 
.7 

2025.1 
2025 . 8 
+0.7 
.4 

Series  A. 


K 


{Frequencies  (observed .  . 
Frequencies  (calculated) 
Differences 
Intervals 


(Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


Cs 


{Frequencies  (observed) . 
Frequencies  (calculated) 
Differences 
Intervals 


1538.2 

1537.2 

-1.0 


1620.5 

1704.0 

1787.2 

1869.6 

1953.5 

1620.5 

1703.8 

1787.0 

1870.2 

1953.5 

0.0 

-0.2 

-0.2 

+0.6 

0.0 

2036.9 
2036.7 
0.2 


83.5      83.2      82.4      83.9      83.4 


1620.2 

1620.9 

+0.7 


1704 . 8 

1704.5 

-0.3 


1787.9 

1788.2 
+0.3 


1871.8 

1871.8 

0.0 


1956.3 
1955.5 
0.8 


2039 . 2 
2039 . 1 
-0.1 


82.0      84.6      83.1      83.9      84.5      82.9 


1624.4 

1624.6 

+0.2 


1706.4 

1706.0 

-0.4 


1789.4 

1873.1 

1957.1 

1789.7 

1873.5 

1957.3 

+0.3 

+0.4 

+0.2 

2041.4 

2041.0 

-0.4 


83.0      83.7      84.0      84.3 


1708.2 

1707.4 

+0.8 


1789.7 

1790.3 

+0.6 


1873.1 

1873.1 

0.0 


1955.7 

1956.0 

+0.3 


2039 
2038 
-0.4 


83.8      81.5      83.4      82.6      83.5 


INTIMATE    STRUCTURE    ON   COOLING. 


87 


Table  31. — General  list  of  fluorescence  bands  in  spectra  of  the  double  uranvl  cMoridea 

at  -185°  C. 


Group 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

and 
series. 

X 

-X103 
X 

X 

^XIO^' 
X 

X 

^X10» 

X 

ixio^ 

A 

2< 

s< 

4 
5 

6 

7' 

fB2 
C2 
D2 
E2" 

Bi 

B2 

C2 

Dx 

D2 

E2" 
fBz 

Ci 

C2 

Di 

D2 

E2' 

E2" 

Ai 

A2 

Bi 

B2 

Ci 

C2 

Di' 

Di 

D2' 

D2 

E2' 

E2" 

Ai 
IA2 

Bi 

B2 

B3 

Ci 

C2 

D,' 

Di 

D2' 

D2 

E2' 

E2" 

Ai 

iA2 

fBi 
B2 
B3 
Ci 
C2 
Di 
Do' 
D2 
El 
E2' 
E2" 
Ax' 
Ax 

A- 

0.6398 
.6330 
.6283 
.6207 
.6110 
.6079 
.6016 

1563.0 
1579.8 
1591.5 
1611.0 
1636.7 
1645.0 
1662.1 



0.6056 
.5991 
.5964 

1651.3 
1669.2 
1676.7 

0.6035 
.6006 

1657.0 
1665.0 

0.6018 
.5990 

1661.7 
1669.4 

.5968 
.5899 
.5791 

1675.6 
1695.0 
1726.9 

.5803 

1723.2 

.5764 
.5721 
.5705 
.5684 
.5662 

1734.9 
1747.9 
1752.7 
1759.4 
1769.3 

.5752 
.5724 

1738.4 
1747.0 

.5733 
.5704 
.5677 

1744.4 
1753.1 
1761.4 

.5731 
.5703 

1745.0 
1753.4 

.5641 

1772.7 

.5624 
.5595 

1778.1 
1787.3 

.5603 

1784.6 



.5573 
.5546 
.5520 
.5489 
.5471 

1794.5 
1803.1 
1811.5 
1821.9 
1827.8 

.5564 
.5526 
.5500 
.5464 
.5452 
.5440 
.5427 
.5412 
.5395 

1797.2 
1809.5 
1818.1 
1830.2 
1834.1 
1838.2 
1842.5 
1847.7 
1853.7 

.5569 
.5542 
.5508 
.5489 

1795.8 
1804.4 
1815.5 
1821.7 

.5524 
.5493 
.5471 

1810.4 
1820.5 
1827.7 

.5461 

1831.0 

.5445 

1836.7 

5444 

1836.9 

.5437 
.5389 

1839.4 
1855.7 

.5420 
.5379 
.5370 
.5345 

1845.1 
1859.0 
1862.0 
1870.8 

.5419 

1845.2 

.5358 

1866.4 

.5354 

1867.6 

.5326 
.5300 
.5277 

1877.7 
1886.8 
1895.0 

.5318 
.5286 
.5260 

1880.4 
1891.8 
1901 . 1 



.5321 
.5297 
.5279 
.5262 
.5250 

1879.5 
1888.0 
1894.3 
1900.4 
1904.6 

.5279 

1894.4 

.5250 
.5234 

1904.8 
1910.6 

.5247 
.5231 

1905.9 
1911.7 

.5223 
.5214 
.5201 
.5191 
.5179 
.5163 
.5137 
.5127 

1914.6 
1918.0 
1922.7 
1926.3 
1930.9 
1937.9 
1946.8 
1950.4 

.5226 

1913.5 

.5206 

1921.0 

.5207 

1920.3 

.5200 
.5155 

1922.9 
1939.9 

.5184 
.5149 
.5141 
.5118 

1929.2 
1941.9 
1945.0 
1953.7 

.5182 

1929.9 

.5124 

1951.6 

.5107 
.5098 
.5073 
.5054 

1957.9 
1961.6 
1971.4 
1978.6 

.5092 
.5059 
.5038 

1963.9 
1976.5 
1984.9 

.5092 
.5070 
.5056 

1963.9 
1972.3 
1977.8 

.5080 
.5056 

1968.7 
1977.9 

.5028 
.5018 
.4989 

1988.7 
1992.7 
2004.5 

.5006 

1997.6 

.5031 
.5007 

1987.6 
1997.2 

.5018 
.4991 

1993.0 
2003.7 

.4979 
.4963 
.4950 

2008.5 
2014.9 
2020.2 

.4982 
.4956 

2007.4 
2017.8 

.4967 

2013.4 

.4967 
.4938 

2013.2 
2025.1 

.4940 

2024.1 

.4926 
.4918 

2030.0 
2033.3 

.4930 
.4916 
.4904 

2028.4 
2034.2 
2039.2 

.4917 
.4902 

2033.8 
2040.0 

8  "R« 

.4857 

2058.9 

88 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  32. — Frequencies  and  intervals  of  fltiorescence  bands  in  the  spectra  of  the  four  double 

chlorides  at  —185°  C. 


Series 

and 

group 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

A* 

Inter- 
val. 

1X103 

Inter- 
val. 

1X103 

Inter- 
val. 

1x103 
A* 

Inter- 
val. 

Bi 

[3 
5 

6 

7 

8 

1636.7 

1795.8 
1879  .'5" 
1963.9 

1803.1 



1886.8 

"k'i'.i" 
84.6 

1809.5 
1976.5' 

82.3 

"s2a" 

83.7 

4X83. C 

84.4 

1968.7 

1971.4 

2058.9 

B, 

'2 
3 
4 
5 
6 
,7 

1563.0 

82.0 

1645.0 

1651.3 

"ss.'e  " 

83.2 

"ssio  " 
"ssis"* 

81.9 

1723.2 
1804  .'4' 
1888.0* 
1972  .'3' 

'81.2   ' 
*83!6" 

"si.'s" 

1726.9 
1810 .4' 
1894.4 
1977  .'9' 

1734.9 

83.5 
"84.'6" 
"83!5   " 

1811.5 
"1895  ."6" 
1978."  6 ' 

"*83."5" 

"ss.'e" 

1818.1 

'igoi.'i' 

'1984  ."9' 

B,  - 

6 

7 

1894.3 
"i977!8' 

83.5 

Ci 

'4 
5 
6 

7 

1747.9 

82.3 

"ma" 
"ks.o" 

1815.5 
1966  .'4" 

"84.'9   " 

1820.5 

1904  .'si 
83.9 
1988.7 

"si.'s" 

1821.9 
'1965  .'9' 

84.0 

1830.2 
1914.' 6 ' 

1997.61 

C2 

^2 
3 
4 
5 
6 
7 

1579.8 

82.3 

"82.'3   " 

"82  .'3" 

"82.'9" 

"82  ."i" 

1657.0 
1738  .'4' 
i82i.'7' 
' 1904.6" 
1987.6 

"si.'i" 
"si.'s" 

"83.'6" 

1662.1 
'1744  .'4' 
*  1827  .'7' 
1910.' 6 " 
1992.7 

1661.7' 
1745.6 

1827.8 

i9ii.'7" 

1993.0 

"83  .'3" 

'"82.'8" 

83.9 
""8l!3" 

1669.2 
'1752  .'7 
1834.1 
1918.' 6* 

"83.'5" 

"si  ."4"' 
"si.'d"' 



Di' 

5 

6 

1838.2 

""84.'6" 

1922.7 

D, 

3 

4 
5 
6 

7 

1665.0 
1747.0' 
1831.0 
1913.5' 
1997  .'2 

1669.4 

84.0 
"83 .'5   " 

"ss.'i  " 
"kzA" 

1676.7 

1759  .'4' 

'1842  .'5' 

'1926  .'3' 

'2668."5' 

"82.'7" 
"83."  i" 

"kk'.s" 

"82.'2" 

82.0 

"si.'o" 

'82.5"' 

"ss.'f" 

1753.1 
'1836  .'7' 
1921.0 
2664.'5 

"83  ."e" 

84.3 
"83  .'5" 

1753.4 
1836.9 
1920  .'3 
'2663  ."7* 

INTIMATE   STRUCTURE   ON   COOLING. 


89 


Table  32. — Frequencies  and  intervals  of  fluorescence  hands  in  the  spectra  of  the  four  double 
chlorides  at  —185°  C. — continued. 


Series, 
and 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

group 

^^X103 

Inter- 
val. 

^X103 

Inter- 
val. 

^X103 

Inter- 
val. 

^X103 

Inter- 
val. 

w 

5 
6 

7 

1847.7 

"83!2   " 
"84!6  " 

1930.9 

2014.9 

D2 

2 
3 

4 
5 
6 

7 

1591.5 

84.1 

1675.6 

85.8 

. . . 

1761.4 

1769.3 

"ss.i" 

"83!2' 

83.7 

"siii' 

.... 
"84!2 


1839.4 
1922.9 
2007.4 

"'83.5 
"'84.5   ' 

1845.1 
'i929!2 
'2613  ."4" 

1845.2 
"i929."9 
"2613  .'4" 

"84!7" 

"ss.s 

1853.7 
1937  .'6 

'2626 !2 

Ej'- 

'4 
5 
6 

7 

1772.7 
1855  .'7' 
1939  .'9 

83.0 
'84!2' 

1859.0 
1941.9 

82.9 

1946.8 

"83!2' 

82.2 

2024.1 

2030.0 

E/' 

2 
3 
4 
6 
6 
7 

1611.0 

84.0 

1695.0 

83.1 

1778.1 

83.9 

1862.0 

1866.4 

84.0 
"'82.'9' 

83.0 

1945.0 

1950.4 

2033.3 

Ai'  7 

2028.4 

2033.8 

Ai 

4 
5 
6 

7 

1784.6 
1867 .6 
1951 .6 
2034.2 

"'83.6' 
"*84.0"' 
"82.6" 

1787.3 
"1870."  8 
"1953.7 

83.5 

82.9 

1957.9 

82.1 

2040.0 



A2 

'4 
5 

6 

7 

1794.5 

""83.'2' 
83.9 

1797.2 

'issoi-i' 

1963.9 

"saii* 

"'83^5   " 

1877.7 

1961.6 

2039.2 

1                1 

90 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  33  —General  list  of  absorption  bands  in  spectra  of  the  double  uranyl 
'  chlorides  at  +20''  C. 


Series  b. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

^-xio' 

A 

Inter- 
val. 

ixio' 

Inter- 
val. 

\  XIO' 
A 

Inter- 
val. 

'    X103 
X 

Inter- 
va  . 

1970.1 

moss's" 
miosis' 

'2i79!6 
'2247.8 

68^4   "' 

70.3 
'76!8 
'68'2' 

71.0X5 

72.0 

1970.1 
2041.2 
2ii3!6 
2185.0 
2256!2 
2329.5 
2400.3 

7l!l 

n.'s' 

"72'6   " 
'7l!2*" 
73.3 

'70^8   " 

71.3X5 

1974.0 
2044.0 

'2ii4!4 
2184.6 

"2253^1 

70.0 
'70a" 
'76!2"' 

69.5 

•70.7X5 
73.0 

1974.2 
2043  is* 
2113.9 

"2i84!3" 

'2255^3 
2327.0* 

"2398!4' 
2471 !o' 

"2539! 7 

69.1 
70.6   " 
70*4   " 

7i!o 

n.i" 

'71.4 

"72'6" 

'esif" 

2603 . 0 
'2675!o 

2606.5 
"2679^5 

2756.8 

Series  b'\ 

2620.9 

71.9 

2692.8 

Series  /3. 

2056.0 

ii.i" 

'72.'2   " 

io.s 

70.9X2 

69.7X3 
71.3 



2127.1 

2199.3 

2269.6 

2411.4 

2620.5 

2691.8 

*  These  bands  were  doubled  occasionally. 


INTIMATE    STRUCTURE    ON    COOLING. 


91 


Table  33. — General  list  of  absorption  hands  in  spectra  of  the  double  uranyl 
chlorides  at  -\-W°  C. — continued. 


(Series  c. 

Potassium 
uranyl  chloride. 

Ammonium 
uianyl  chloride. 

Rubidium 
uranyl  chloride. 

Cspsium 
uranyl  chloride. 

Ixw 

Inter- 
val. 

{xw 

Inter- 
val. 

^X10» 

Inter- 
val. 

[xio' 

A 

Inter- 
val. 

1985.2 
2053 .8 
'2125.4 

68.6' 
'7i!6     " 

■71.2X7 

69.5 

1988.5 
2057.5 
2126.6 

69.0 

"esis"' 

1989.1 
2057.6 
2130.4 

68.*6'    ' 
■72!8'*" 

1993.1 
'2064.4 

"n.'s'  ' 

68.9 
70.8X6 

2199.3 

2623 . 8 
2693.3 

2624.5 

(Series  7. 

1997.0 
2067.4 
"2i37!6 

■76.4'    ' 
76!6" 

70.5X6 

2001.6 
2070 .6 
'2142.' 6 

69.0*' 
72.'6 

70.4X6 

72.0 

2001.0 
2070.5 
2141.3 
2209  ."6 

69.5 

70.8 

67.7 

>71.6X3 

69.4 

2423.7 
2493.1 

2560.2 

2565.1 

2637.1 



71.5 

2708.6 

Series  d' . 

2071.3 

70.4X2 

72.8 
'76!6'' 
'72!o*' 

76!6  ' 
'72!i   " 

'es!!"" 

2212.2 

2284.0 



2354.6 

2426.6 

2496.6 

2568.7 



2638.9 
'27i2!2" 

2642.0 

2636.8 

73.3 

2713.7 

92 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  33. — General  list  of  absorption  hands  in  spectra  of  the  double  uranyl 
chlorides  at  +£0°  C. — continued. 


SeHes  d. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Csesiimi 
uranyl  chloride. 

^xio. 

Inter- 
val. 

^XIC 

Inter- 
val. 

ixic 

Inter- 
val. 

i-xic 

Inter- 
val. 

2004.3 
2075.1 
'2146  A 

2007.1 

'73.'6'    ' 
69.1 

►71.9X2 

71.7 

2004.9 
2076.3 
'2145  .'5' 

'n.'i"" 

'69!2     * 

70.8 

2080.1 

71.3 

2149.2 

2218.9 

'69.'6 '" 

"72  .'i*' 
'egis"" 
'71:9" 

2288.5 

2293.1 
'2364.' 8 ' 
'2435!4' 
'2563.9' 
■2577."7' 

2359.9 

70.6 

2432.0 

68.5 

2501.8 

73.8 

2573.7 

Sene 

hd". 

2008.9 

'n.'i* 

2013.7 

70.8X3 

2080.1 

69.4 

2149.5 

2221.8 
2291.9 
2361  .'3" 
2431  is' 

'2563! i" 

2574.8 

2226.0 

70.1 

69.4 

70.2 

71.6 

71.7 

Seri 

es  e. 

2021.4 
2696.9' 
'2i6i!6 

69!5'    ' 
'76!i"' 

70.2X4 

2023.3 
2094.6 

iies.'s' 

'76^7' " 

'7i!6'    ' 
71.7X2 
70.9 

69.6X3 

73.0 

2025.3 
'2694.'9' 
2166  .'4" 
2235.6' 

eg.'e" 
'n.'s'" 

'69!2" 
71.3X5 

2025.6 
'2694  .'7' 

'2165  .'6' 

2237.0 



2310.0 

2378.2 

'2448.6' 

'2526  .'2' 

69  .'i" 
'76.9'    ' 
'72."4"" 
'73.6'    ' 
'68.'2"" 
'69.*8"    ' 

72.2 

2309.0 
'2379  .'9' 

2442.0 

2588.7 

2592.0 

2661.7 

INTIMATE    STRUCTUHE   ON   COOLING. 


93 


Tabuj  33. — General  list  of  absorption  hands  in  spectra  of  the  double  uranyl 
chlorides  at  -\-20°  C. — continued. 


Senea  e". 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Csesiimi 
uranyl  chloride. 

ixi03 

Inter- 
val. 

ixio. 

Inter- 
val. 

ixic 

Inter- 
val. 

ixio« 

Inter- 
val. 

2173.6 

71.0 

'76;i*  " 

Yo'.q" 

'  * 

2244.6 

2248.5 
2318.0 

69.6 



•  * 

2313.0 
2381.6" 
2452 .8 
2524.6 

68.6'"' 

'nii" 

7i!2" 

2314.6 
'2384!6' 
2455 !2' 
2527  ."4' 

67.7 

71.0X2 

67.8 

70.6 
"72."2*    " 

|71.3X3 

2460.0 
2527."  8 ' 





2741.2 



/Series  a. 

2037.1 

70.6X8 
72.6     * 









2602.2 

■ 

2674.2 

Series  a". 

2329.4 
2398.7 

2333.7 

69.3 
70.3X2 

70.2 

2403.9 

67.7 

2471.6 

70.5 

2539.4 

2542.1 

Table  34. — General  list  of  absorption  hands  in  spectra  of  the  dovble 
uranyl  chlorides  at  —186°  C. 


Series  h'. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

CfiBsium 
uranyl  chloride. 

ixiO' 

A 

Inter- 
val. 

1X103 

A 

Inter- 
v^. 

A 

Inter- 
val. 

lxio» 

A 

Inter- 
val. 

2029.1 
2160."  8 ' 
2176  ."9' 

2045.3 

'7i.'i    " 
'76.' i" 



71.7 

2116.4 

70.1 

2186.5 

94 


FLUORESCENCE   OF  THE   URANYL   SALTS, 


Table  34. — General  list  of  absorption  hands  in  spectra  of  the  double  vranyl 
chlorides  at  —185°  C. — continued. 


Series  bi. 

Potassium 
urany    chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

Ixw 

Inter- 
val. 

Ixi^ 

Inter- 
val. 

Ixw 

Inter- 
val. 

^xio^ 

A 

Inter- 
val. 

2038.6 

71.5 

2109.0 

71.2 

2180.2 

70.7 

2250.9 

71.9 

2322.8 

71.2 

2394.0 

72.8 

2466.8 

70.5 

2537.3 

72.7 

2609.0 

1 

Series  6/'. 

2044.2 

70.7 

2114.9 



70.0 

72.0X2 

72.5 

69.9X2 

72.4 



2184.9 

2328.8 

2401.3 

2541.0 



2613.4 

73.0 

2686.4 

-Series  62'. 

2045.5 

2051.6 

71.3' " 

70.6 

69  .'5'" 
'71.0'"' 
'70.'7"' 
'7l!6'" 
'69!2   " 

71.4 

2116.9 

2122.9 

70.8 

2187.7 

2193.5 

2263.0 

2334.0 



2404.7 

2476.3" 

2545.5 

INTIMATE    STRUCTURE    ON    COOLING. 


95 


Table  34.— General  list  of  absorption  bands  in  spectra  of  the  double  uranyl 
chlorides  at  -185°  C— continued. 

iSeries  bj. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidiimi 
uranyl  chloride. 

Csesiiun 
uranyl  chloride. 

ixio' 

Inter- 
val. 

\xw 

Inter- 
val. 

ixio' 

Inter- 
val. 

ixio- 

Inter- 
val. 

2043.6 

2184.0 
'2254.3' 
2325 le' 

2050.4 

70.1 

71.0 

2121.4 



70.3 

70.2 

* '  ■ 

2191.6 

70.3 

71.1 

2262.7 

2268.6 

[71.0x2 

70.1 
69  .'s" 

71.3 

2410.5 

2480.6 

2550.4 

Series  62". 

2051 . 1 

71.6 



2122.7 

70.4 

2193.1 

72.8 

2265.9 

72.3 

2338.2 

70.5 

2408.7 

70.3 

2479.0 

71.1 

2550.1 

72.6 

2622.7 



Series  63. 

2056.5 

70.4X2 

71.5X3 

70.6 

71.9X2 

2061.9 

70.6X3 
70.9X2 

2197.3 

2273.8 

2411.9 

2415.5 

2482.5 

2626.3 

Series  C/. 

2064.3 

*76;6  " 
'76.'6  " 

2134.9 

2204.9 

■ 

96 


FLUORESCENCi;  OF  THE    URANYL   SALTS. 


Table  34. — General  list  of  absorption  bands  in  spectra  of  the  double  uranyl 
chlorides  at  —185°  C. — continued. 


Series  Ci. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

ixic 

Inter- 
val. 

ixio= 

Inter- 
val. 

ixl03 

Inter- 
val. 

ixio' 

Inter- 
val. 

2059.— 

72.0 
68.7 

2067.8 

[70.3X3 

2131.3 



2200.0 

72.0 
69.'9      " 
69.5 

[71.6X4 

2272.0 

2278.7 

2349.7 

2421.3 

"2491.6' 



2560.5 

■71.0*" 

"n.'e" 

'76.'3" 

'es.'o'  " 

2341.9 

2411.4 

2997.6 

Series  C<i  . 

2141.3 

71.1 
'76.'7"" 

2212.4 

2264.2 
'2332!7' 
2404.0 

2283.1 

68.5 

71.3 
69.2X2 

2542.3 

Series  Ci. 

2057.6 
2197.3 

69.'8*" 

"m.ki' 

70.3X2 

2064.7 
2136.5 
"2207.3' 
'2278.3' 
'2348.'i' 

'n.'s" 

2064.7 
2134.5 

69.8 

70.8 

"n.'o'  ' 

2265.4" 

70.9 

'2337!8' 

69.8 

2356.0 

'n.'s'"' 

70.3 
'69.3"  " 

70.9 

2419.0 

2427.8 

70.9 

2489.9 

2498.1 

71.7 

2561.6 

2567.4 

71.4 

2633.0 

INTIMATE   STRUCTURE    ON   COOLING. 


97 


Table  34. — General  list  of  absorption  hands  in  spectra  of  the  double  uranyl 
chlorides  at  —185°  C. — continued. 


Series  Ca". 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

ixl03 

Inter- 
val. 

Ixw 

Inter- 
val. 

ixic 

Inter- 
val. 

ixio. 

Inter- 
val. 

2346.1 
2414 .9 

2352.4 

69.7X3 
72.9 

68.8 
U9.IX2 



. 

?/>53.0 

2561.5 

2634.4 

72.0 

2706.4 

Series  di. 

2068.8 
'2139.5 
'  2208  .'5' 

2278  .'5* 

2075.4 

70.7 

70.3 

2145.7 

69.0 

69.2 
72.7X2 

70.4X3 

2214.9 

70.0 

2360.2 

2571.4 

Series  d/'. 

2006.8 

2009.6 

72!6" 

■TO^s"" 
'66.7'" 
72.2 

70.5X2 

69.6 

71.1 

2077.9 

2081.6 

71.0 

2148.9 

2152.4 

69.3 

2218.2 

2219.1 

70.3 

2288.5 

2291.3 

70.6 

2359.1 



71.8 

2430.9 

2432.3 

71.1 

2502.0 

2501.9 

71.2 



2573.2 



72.3 





2645.5 

98 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  34. — General  list  of  absorption  bands  in  spectra  of  the  double  uranyl 
chlorides  at  —186°  C. — continued. 


Series  d^'. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

ixl03 

Inter- 
val. 

1X103 

Inter- 
val. 

1X103 

Inter- 
val. 

1X103 

Inter- 
val. 

. 

2221.4 

'71.2     * 
'76.'7' 

71.3X3 

2086.2 

'ijiseii 

2223.7 
"2296 ]2* 
'2364  .'4' 

2436  .'4' 

'76.'2   "' 
'67 .'3"    ' 
'72.'5*" 
'68.'2"" 
'72.'6"    " 
'72.'i""* 

2292.6 

2363.3 

2577.3 

2508.6 

2579.3 

Series  d^. 

2079.0 
"2148.9* 

2217.1 

2287.6 
*2356.*i 

2429 !2* 

69.9 

68.2 

2229.2 

'n.'e    " 
"esie" 
"n.'i"  " 

'72.'4""' 

'n.'i" 

70.6 

2300.8 

68.6 

2369.4 

73.1 
69.8X2 

2440.8 

2613.2 

2668.7 

2584.6 



Senes  d^". 

2016.1 

, 

70.1 
72.6'*' 

2086.8 

"&k'.7" 

Yl.'b" 

2086.2 
2158.2' 

2092.7 
'2163.' 8 

'7i."i""" 
'69 .'3  " 
ii'.k" 
'73  ."i" 

'66  .'7" 

2155.6 

2227.0 

2^33.1 

71.0 

2298.0 

2304.9 

70.3 

2368.3 

'2378!6 

69.6 
70.7X3 

2437.9 

2444.7 

2650.0 

INTIMATE    STRUCTURE    ON    COOLING. 


99 


Table  34.— (General  list  of  absorption  hands  in  spectra  of  the  double  uranyl 
chlorides  at  -186"  C— continued. 

Series  dt. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

ixio. 

Inter- 
val. 

ixio- 

Inter- 
val. 

-^X103 

Inter- 
val. 

ixic 

Inter- 
val. 

2014.0 

70.6X2 

69.2X3 
73.6 

2155.2 



2362.7 
2436  is' 

Series  e\'. 

2021.6 

72.0 

69.8X2 

71.1 

2093.6 

2233.1 

2304.2 

70.5 

2374.7 

71.6 

2446.2 

71.1 

2517.3 

70.2 

2587.5 

Series  ei. 

2092.7 

69.4 
'76."9"    ' 
'76.'4'" 

72.'6*' 
'69  .'6'" 
'76.'8"' 

70.9X2 

2162.1 

2166.8 
'2236  .'7' 

'2369  .'6' 

'2378  ."7" 
2450  .'4* 

69.9 

2229.4 

69.9X2 

71.9 
'69.'6   ' 
71 A   " 

2233.0 
'2363.4 
"2376  .'6 
2445.0 
2515.' 8 ' 

2657.5 

72.3 

68.7 

2369.1 
2441.0 
2510.6 
2582.0 

71.9 

100 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  34. — General  list  nf  ahsorpiion  bands  in  spectra  of  the  double  uranyl 
chlorides  at  —185°  C. — continued. 


Series  &i  . 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloride. 

Rubidium 
uranyl  chloride. 

Csesium 
uranyl  chloride. 

ixi03 

Inter- 
val. 

^XIO' 

A 

Inter- 
val. 

1X103 

Inter- 
val. 

^X103 
A 

Inter- 
val. 

2023.4 
'2094^5 
2165.0 

2029.6 

'70.8" '" 

70.2 
'68.0" 

71.7 

71.1 

2100.4 

70.5 

70.3X2 

69.4 
71.7X2 

2170.6 

2238.6 

2305.5 
'2374 .9 

2310.3 

2518.3 

Series  e^. 

2030.7 

70.3 

2101.0 

71.5 

2172.5 

69.7 

2242.2 

71.0 
69.5' 

[71.7X3 

2313.2 

2314.0 
2383 .0" 
2525.3 
'2594.7" 

;;;;;;;; 

69.0 

[71.2x2 

i 

69.4 

2382.7 

2597.8 

Series  e-z". 

2031.0 

2034.1 

"71.'4'' 

70.6 

68.9'"" 
'72.8"" 

70.8 

'70.6X2 

71.4 

2102.4 

2105.5 

72.0 

2174  A 

2176.1 

67.8 

72.7X2 

72.2 

2242.2 

2245.0 

2317.8 

2387.5 

2388.6 

2459.7 

71.0 

2530.7 

2529.7 

INTIMATE    STRUCTURE    ON    COOLING. 


101 


Table  34. — General  list  of  absorption  bands  in  spectra  of  the  dovhle  uranyl 
chlorides  at  —185°  C. — continued. 


Series  a/. 

Potassium 
uranyl  chloride. 

Ammonium 
uranyl  chloiide. 

Rubidium 
uranyl  chloride. 

Caesium 
uranyl  chloride. 

,-Xl03 

A 

Inter- 
val. 

^X103 
A 

Inter- 
val. 

^X103 

Inter- 
val. 

{xw 

Inter- 
val. 

2036.9 

70.6   ■' 
70;7'" 

71.1X3 

71.9 
'70'2     ' 

2038.1 
"2168.4' 
'2179.1 

2249.7 
'2322^3 

2393.5 

76.'3'" 
70.7'" 
70.6"  ' 
72.6 
'7l!2'" 

70.4X2 

2107.5 

2178.2 

2391.5 

2463.4 

2533.6 

2534.3 

Series  ai. 

2038.5 

71.5 

2109.0 

71.2 

2180.2 

70.7 

2250.9 

71.9 

2322.8 

71.2 

2384.4 
2456.4 
2525.6 
2594!? 

72.0 
69.2 
69.  T" 

2394.0 
'2466.8' 
2537^3 
2609 . 0 

72.8 

70.5 

71.7 

Series  ai. 

2038.1 
'2108'5' 
'2178!9" 

2044.2 

'70^7'    ' 
IQ.o" 

2045.3 
'2ii6.'4' 
2i86!5" 

'7i!l   " 
'76!i 

70.4 

2114.9 

70.4 
70.4X2 

2184.9 

2319.6 

Series  Oi" . 

2391.9 

[70.7X2 
74.2 

2533.3 
'2607!5' 



VI.  THE  POLARIZED  SPECTRA  OF  THE  DOUBLE  CHLORIDES 
AND  DOUBLE  NITRATES. 

The  polarization  of  the  fluorescent  light  from  crystals,  first  noted 
by  Grailich  in  1857/  has  since  been  studied  by  Maskalyne/  von  Lom- 
mel/  E.  Wiedemann/  Sohncke/  Schmidt/  H.  Becquerel/  and  Pochet- 
tino.^ 

With  the  exception  of  the  work  of  Becquerel  on  the  ruby,  in  which 
low  temperatures  were  employed,  the  authors  cited  above  dealt  chiefly 
with  fluorescence  of  the  usual  type,  consisting  of  broad  bands.  In 
such  cases  the  most  that  can  be  done  is  to  determine  the  direction  of 
vibration  and  estimate  the  proportion  of  polarized  light. 

The  uranyl  salts  afford  a  much  more  favorable  field  for  such  investi- 
gations. Well-formed  crystals  of  certain  of  these  salts  show  a  marked 
pleochroism.  When  viewed  through  a  Nicol  prism  their  color  changes 
from  a  yellow-green  to  a  very  pale  yellowish-white  when  the  plane  of 
the  Nicol  is  turned  through  90°.  In  the  case  of  the  double  chlorides  of 
uranyl  (i.  e.,  UOaCl2-2NH4Cl-|-2H20;  U02Cl2-2KCl-|-2H20;  UOzClz' 
RbCl+2H20;  andU02Cl2-  2CsCl),  these  changes  of  color  are  connected 
with  striking  and  significant  variations  in  the  fluorescence  and  absorp- 
tion spectra,  and  this  is  true  also  of  certain  of  the  double  nitrates. 

These  double  chlorides,  as  has  been  shown  in  Chapter  V,  differ  from 
the  other  uranyl  salts  thus  far  studied  in  the  greater  degree  of  resolu- 
tion exhibited  by  their  spectra  at  +20°.  The  further  resolution 
effected  by  cooling  the  crystal  to  the  temperature  of  liquid  air  is  in 
general  the  same  for  all;  i.  e.,  the  bands  are  resolved  into  doublets  the 
components  of  which  in  some  cases,  particularly  noticeable  in  the 
absorption  spectra,  show  indications  of  further  complexity.  The 
doublets,  moreover,  are  polarized,^  the  planes  of  vibration  of  the  com- 
ponents being  at  right  angles  to  one  another,  so  that  two  entirely  dis- 
tinct spectra  of  fluorescence  and  absorption  may  be  observed  by  the 
use  of  a  Nicol  prism. 

For  the  study  of  these  remarkable  phenomena  the  apparatus  depicted 
in  figure  70  was  devised. 

Within  the  collimator  of  a  spectroscope  of  constant  deviation  a 
rhomb  of  calcite  R  was  so  mounted  as  to  give  two  vertically  displaced 
images  of  the  slit,  and  these  by  suitable  adjustment  of  the  length  of  the 
slit  could  be  rendered  contiguous  without  overlapping. 

1  Grailich,  Krystall-optische  Untersuchungen,  "  G.  C.  Schmidt,  Wiedemann's  Annalen,  lx,  p. 

Wien,  1858.  740. 

«  Maskalyne,   Proc.   Royal    Society,    xxviii,  '  H.  Becquerel,  Comptes  Rendus,  cxliv,  p. 

p.  479.  671. 

*von  Lommel,  Wiedemann's  Annalen,  viii,  ^Pochettino,  Nuovo  Cimento  (v),  18.     1909. 

P-  634.  9  Nichols  and  Howes,  Proce.  Nat.  Acad.  Sci. 
E.  Wiedemann,  Wiedemann's  Annalen,  ix,  p.  i,  p.  444,  1915;   and  more  fully  in  Phys. 

.„  ^^^?-   „,.    ,  Rev.  VIII,  p.  364.     1916. 

'  Sonncke,  Wiedemann's  Annalen,  lviii,  p.  417. 

102 


POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


103 


The  crystal  C  was  mounted  before  the  sUt  and  turned  about  the  axis 
of  the  colUmator  until  the  planes  of  vibration  of  the  transmitted  light 
coincided  with  planes  of  transmission  of  the  rhomb. 

For  the  study  of  fluorescence,  the  Ught  from  a  carbon  arc  A,  after 
passage  through  the  condensing  lens  L,  the  water-cell  TT,  and  a  light- 
filter  F,  was  employed  for  excitation.  The  filter  was  opaque  to  hght 
of  a  wave-length  greater  than  0.45^,  so  that  the  fluorescence  appeared 
on  a  black  background.  When  absorption  spectrographs  were  required 
a  pale-blue  screen  was  substituted,  and  the  carbon  arc  was  replaced  by 
a  1,000-watt  nitrogen-filled  tungsten  lamp. 


Fig.  70. 

Many  crystals  were  produced  before  any  were  found  which  gave 
complete  separation  of  the  two  polarized  components.  A  mere  inspec- 
tion of  the  crystals  was  not  a  sufficient  criterion;  but  when  trans- 
mitted light  polarized  parallel  to  one  of  the  planes  of  vibration  of  the 
crystal  was  used,  the  presence  of  only  one  of  the  two  absorption  spectra 
was  found  to  afford  a  very  delicate  test,  both  for  the  adjustment  of  the 
apparatus  and  the  homogeneity  of  the  crystal.  In  accordance  with  the 
usage  adopted  we  shall  call  that  component  of  the  spectrum  due  to 
vibrations  in  the  more  transparent  direction  of  the  crystal,  the  white 
component,  while  the  component  at  right  angles  to  this  will  be  designated 
as  the  green  component.  The  stronger  fluorescence,  as  might  be  expected, 
is  that  of  the  green  component,  since  Ught  polarized  in  that  plane  is 
more  strongly  absorbed. 

The  four  double  chlorides  upon  which  observations  were  made  crys- 
tallize in  triclinic  plates.  These  were  so  mounted  that  the  flat  faces 
were  at  right  angles  to  the  transmitted  light. 

The  flat  faces  of  the  potassium,  ammonium,  and  rubidium  uranyl- 
chloride  crystals  correspond  to  the  (c)  crystallographic  face,  while  the 
flat  face  of  caesium-chloride  crystals  corresponds  to  the  (6)  crystallo- 
graphic face.  The  caesium  chloride  crystallizes  in  gypsum-fike  plates, 
which  were  mounted  with  the  longest  (c)  crystallographic  axis  vertical. 
Since  the  plane  of  polarization  of  the  white  Ught  is  also  vertical  within 


104  FLUORESCENCE    OF  THE    URANYL    SALTS. 

a  degree  or  two,  light  vibrating  horizontally  is,  in  this  arrangement, 
less  absorbed  than  light  vibrating  vertically.  As  to  the  direction  of 
vibration  of  the  white  light  within  the  crystal,  it  can  be  said  to  be  more 
nearly  parallel  to  the  (a)  crystallographic  axis  than  to  the  (b)  axis. 
Rubidium  chloride  crystallizes  in  long  six  sided  plates.  As  mounted, 
plane  polarized  light  was  transmitted  most  freely  when  the  direction 
of  vibration  was  parallel  to  the  (a)  crystallographic  axis.  Potassium 
and  ammonium  chlorides  crystallize  in  thin  plates  which  approximate 
more  nearly  the  hexagon  in  form.  Examination  of  the  transmitted 
light  with  the  aid  of  a  Nicol  shows  that  the  same  relations  exist  between 
the  directions  of  vibration  and  the  crystallographic  axes  as  for  the 
rubidium  chloride.^ 

Two  polarized  fluorescence  spectra  are  always  present,  provided  the 
crystal  is  mounted  as  previously  described.  It  is  a  remarkable  fact  that 
these  spectra  remain  unchanged,  whether  the  exciting  light  is  unpolar- 
ized  or  is  polarized  in  a  white  or  green  direction,  or  any  other  direction. 
Their  character,  moreover,  appears  to  be  independent  of  the  direction 
from  which  the  exciting  light  enters  the  crystal.  This  is  in  agreement 
with  a  general  principle  established  by  the  study  of  fluorescence 
spectra,^  that  the  character  and  location  of  a  fluoresecnce  band  is 
independent  of  the  nature  of  the  excitation.  Changes  in  the  polarized 
spectra  occur,  however,  as  might  be  expected,  if  different  crystallo- 
graphic faces  are  placed  at  right  angles  to  the  axis  of  the  collimator. 

Although  visual  observations  were  made,  the  spectra  were  mapped 
for  the  most  part  from  the  photographic  plates.  Occasionally,  the 
fluorescence  and  a  portion  of  the  absorption  spectrum  could  be  photo- 
graphed simultaneously  to  advantage,  but  more  often  different  screen- 
ing and  various  times  of  exposure  were  necessary  in  order  to  bring  out 
different  regions  of  the  absorption.  The  exposures  varied  in  time  from 
30  seconds  to  an  hour. 

A  STUDY  OF  TYPICAL  GROUPS  OF  BANDS  FROM  THE  FLUORESCENCE 
AND  ABSORPTION  SPECTRA  AT   +20''  C. 

In  the  study  of  the  spectra  of  the  double  chlorides  described  in  Chap- 
ter V,  it  has  been  shown  that  each  group  consists  of  5  members  and  that 
each  of  these  bands  is  double.  Since  polarization  effects  a  resolution 
or  separation,  we  should  expect  in  general  to  find  5  components  in  each 
polarized  fluorescence  group.  In  that  chapter  the  bands  of  one  fluores- 
cence group  have  been  designated  as  B,  C,  D,  E,  and  A,  and  the  same 
nomenclature  will  be  employed  here. 

A  typical  fluorescence  group  for  each  of  the  four  salts  is  indicated 
in  figure  71 .  The  bands  above  the  horizontal  line  are  the  green  polar- 
ization components  (Bg,  Cg,  etc.) ;  those  below,  the  white  polarization 

^  The  excellent  specimens  which  were  finally  utilized  in  this  investigation  we  owe  to  the  per- 
sistent and  skillful  efforts  of  Mr.  D.  T.  Wilber. 

*  Nichols  and  Merritt,  Physical  Review,  series  i,  27,  p.  373.     1908. 


POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


105 


components  (B^,  C^,  etc.).  The  lengths  of  the  bands  give  an  approxi- 
mate idea  of  their  intensities,  although  the  difference  in  intensity 
between  a  strong  C  band  and  a  weak  A  band  can  not  be  shown  to 
advantage  in  such  a  diagram.  The  positions  of  the  crests  of  the  bands 
are  taken  from  the  observed  values,  to  be  found  in  table  35,  but  the 
width  and  form  of  the  bands  are  more  or  less  arbitrary,  being  the 
expression  of  a  judgment  based  on  a  large  number  of  observations. 


POLARIZED     FLUORESCENCE     GROUPS  -1-20' 

URAHYL    POTASSIUM    CHLORIDE  URAHYL    AMMONIUM    CHLORIDE 


WHITE 


rim. 


URAHYL    RUBIDIUM    CHLORIDE 


GREEN 


aRIIN 


WHITE 


! 


y      A 


URAHYL   CAESIUM    CHLARUDE 

C 


WHITE 


Fig.  71. 

From  this  figure  it  will  be  seen  that  bands  C,  E,  and  A  of  uranyl. 
potassium  chloride  appear  as  doublets,  polarized  at  right  angles. 
Band  B  has  no  green  component  visible,  but,  as  will  be  shown  in  a 
subsequent  paragraph,  at  — 185°  a  green  component  is  present,  which 
lies  nearer  the  red  than  B^.  Bands  Cg  and  C^  are  the  two  components 
of  band  C,  while  no  component  of  band  D  has  been  found  on  the  white 
side.  Bands  E  and  A  are  also  well  resolved;  the  white  component  of 
band  E  is  of  longer  wave-length  than  the  green  component,  while  the 
white  components  of  C  and  A,  and  probably  of  B,  are  of  shorter  wave- 
length than  their  respective  green  components. 


106  FLUORESCENCE   OF  THE   URANYL   SALTS. 

The  uranyl  ammonium  chloride  group  shows  a  strong  similarity  to 
the  preceding  group.  All  except  band  B  appear  as  polarized  doublets. 
Components  D^  and  A^  were  discerned  only  with  the  greatest  diffi- 
culty. 

The  uranyl  rubidium  chloride  group  is  very  similar  to  the  uranyl 
potassium  chloride  group.  Band  Bg  is  missing,  but  as  in  the  potassium 
chloride,  there  is  a  —185°  component  to  the  red  of  B^.  Component 
Cw  has  a  position  nearer  Dg  than  has  C^  in  the  preceding  spectra. 
This  is  also  the  condition  existing  in  the  csesium-chloride  spectrum, 
and  it  is  possible,  since  no  D^  component  is  visible  in  either  spectrum, 
that  D^  is  very  dim,  and  hidden  in  C^. 

Uranyl  caesium  chloride  gives  the  most  satisfactory  set  of  fluores- 
cence bands,  since  both  components  of  band  B  are  present,  and  the 
C,  E,  and  A  components  are  very  well  separated.  It  is  interesting  to 
note  that  Bg  is  of  longer  wave-length  than  B^,  as  is  the  —185*^  com- 
ponent of  Bg  in  the  preceding  salts. 

It  has  been  previously  stated  that  the  absorption  spectra,  like  the 
fluorescence  spectra,  are  composed  of  series,  which  begin  with  the 
bands  which  terminate  the  fluorescence  series.  The  absorption  bands 
which  lie  nearest  the  fluorescence  region  can  also  be  arranged  in  recur- 
ring groups.  The  absorption  series  will  be  designated  h,  c,  d,  e,  a; 
since  they  join  the  B,  C,  D,  E,  and  A  fluorescence  series,  respectively. 
The  e  and  A  series  are  the  strongest  in  the  reversing  region,  but  grad- 
ually vanish,  while  the  D  series  becomes  stronger  toward  the  ultra- 
violet. Figure  72  gives  a  typical  absorption  group  for  each  of  the  four 
salts.  As  before,  the  components  above  the  line  belong  to  the  green ; 
those^  below  to  the  white  polarization. 

By  comparing  the  uranyl  potassium  chloride  absorption  group  in 
figure  72  with  the  fluorescence  group  of  the  same  salt  in  figure  71,  it 
will  be  seen  that  there  is  no  hg  component  present,  as  there  was  no 
Bg  component  present,  but  that  c^,  dg^  eg,  and  a^,  corresponding  to 
series  Cg,  Dg,  Eg,  and  Ag  are  present  and  that  there  are  no  other  series 
represented.  Although  the  relative  intensities  of  the  absorption  com- 
ponents are  almost  reversed  when  compared  with  the  relative  intensi- 
ties of  the  fluorescence  bands,  the  same  spacing  exists  between  the 
green  components  of  both  fluorescence  and  absorption.  In  the  white 
polarization  group,  c^  corresponds,  in  position,  to  C^,  and  e^  to 
E^,  while  6„  a^  serves  both  B^  and  A^  series  in  the  following  way:  B^ 
is  the  first  member  of  each  fluorescence  group,  while  A^  is  the  band 
of  the  preceding  group  which  is  nearest  to  B^.  As  the  fluoresence 
intervals  of  both  the  A  and  B  series  are  approximately  83  frequency 
units,  and  A^  is  12  units  distant  from  B^,  the  reversing  band  of  the  a„ 
series  must  coincide  with  the  second  member  of  the  K  absorption 
series,  since  it  is  71  units  from  the  reversing  band  B^  or  h^.  The  d^ 
component  is  absent,  as  is  D^,  and  there  are  no  superfluous  series. 


I 


POLARIZED    SPECTRA   OF   DOUBLE   CHLORIDES. 


107 


The  absorption  group  of  the  uranyl  ammonium  chloride  is  very 
similar  to  that  of  the  potassium  chloride.  Again,  the  hg  component, 
like  the  Bg  component,  is  absent,  but  the  other  fluorescence  series  are 
represented  by  absorption  series,  save  that  no  component  of  d  was 
found  to  join  the  very  weak  D^  fluorescence  band. 

Uranyl  rubidium  chloride  shows  a  grouping  analogous  to  that  of  the 
potassium  and  ammonium  chloride,  while  the  uranyl  caesium  chloride 
group  is  only  slightly  different. 

A  bg  series  is  present,  which  is  properly  related  to  the  Bg  series,  so 
that  hg  and  by,  are  the  same  relative  positions  as  are  Bg  and  B^. 


POLARIZED  ABSORPTION  GROUPS 


+ao' 


URANYL  POTASSIUM    CHLORIDE 


ORSEN 


WHITE 


URANYL  RUBIDIUM    CHLORIDE 


Gw       CLw  ^w 


URANYL  AMMONIUM  CHLORIDE 


WITTE 


WHITE 


Cw      ^w 


Fig.  72. 


No  green  polarized  component  joins  the  Cg  component.  The  dotted 
line  shows  where  an  absorption  component  would  have  to  be  placed  to 
have  the  proper  relation,  according  to  our  theory.  The  Ca  band  is 
evidently  complex,  c^  is  present,  however,  as  a  single  band,  and  the 
d,  e,  and  a  components  occupy  positions  which  agree  with  their  corre- 
sponding fluorescence  components,    bw  and  aw  are  here  separate. 


108 


FLUORESCENCE    OF   THE    URANYL   SALTS. 


A  DETAILED  STUDY  OF  THE  RELATION  BETWEEN  FLUORESCENCE 
AND  ABSORPTION  SERIES. 

In  figure  73  are  indicated  2  complete  fluorescence  groups  and  2 
complete  absorption  groups  for  each  of  the  8  spectra.  The  remark- 
able fact  is  that  although  no  observed  fluorescence  bands  have  been 
omitted  which  fall  within  the  frequency  numbers  plotted,  each  fluores- 
cence series  has  its  properly  related  absorption  series,  and  with  the  excep- 
tion of  the  complex  Cg  series  of  the  caesium  chloride  not  a  superfluous 


tsloo 

1          isloo          1          aoloo 

1          21I00          1 

c 

QREEN 

imANYL     POTASSIUM    CHLORIDE 

'u  ^'U  1  f 

+20  • 

e  a   c    d    e  a,  c    d 

i  1  !  1 

1    1 

nil     III 

e     ha  c       e     hoL  c 

]   i    i 

c 

6RIEN 

URANYL    AM 

< 
D 

1      1     1 

1         1 
MONIUM     CHLORIDE 

^ir:   it 

III           1 

e  CL    c     d   e  a.   c    <Z 

i    1     i     1     !    1     1     i 

B 
WHITE 

C               ,      '^               be 

E                             E      A  1 
1                               II! 

1 1  ( r  1 1 1 1 

e    ha     c      e    ha    c 

\   \    \    \  \    \ 

C 
QREEN 

URANYL    RU 

it:  ' 

1  1 

BIDIUM    CHLORIDE 

^       EA          <;      f 

W    III    1 

ecb    c     d    ea    c     d 

i     i       i     1   i 

B 
WHITE      1 

I     A    1                t    A 

III                 II 

i 

II      IN 

e   ah      c      e  ah      c 

|i     1     Ml     j 

B 
GREEN     1 

URANYL     CA 

Tt  1 

ESIUM    CHLOt 

1   ■»  ! 

J 

1    .1 

1     (     1    1     1 

e  ah    c    d  e  ah    c   d 

i  1!     !    !    Mi     1    : 

B 
WHITE 

1  !  1        \  \       • 

KIII'M'  nil'  I' 

e  ah      c     e  ah      c 

Ml        M   ' 

isloo 

1              I»i00             1              20JOO 

III        1    1 
1     21I00     1 

Fio.  73. — Polarized  bands  of  fluorescence  and  absorption;  four  contiguous  groups  showing  the 
relation  between  the  green  and  white  components  at  +20°.  Dotted  lines  show  computed 
positions  of  absorption  bands.  Solid  lines  above  the  base  indicate  fluorescence;  below  the 
base,  absorption. 

absorption  series  is  present.  Fluorescence  bands  are  designated  by  the 
solid  lines  above  the  horizontal,  and  absorption  bands  by  the  solid 
lines  below  the  horizontal.  The  dotted  lines  above  the  absorption 
bands  represent  the  hypothetical  positions  of  absorption  bands,  com- 
puted in  the  following  manner : 

The  average  interval  for  the  series  in  question  was  computed  from 
all  available  observations  on  the  bands  which  belong  to  it,  carefully 
weighted.  A  hypothetical  position  for  the  band  in  the  reversing  group 
was  then  found  by  adding  this  interval  to  the  average  of  the  observa- 
tions on  the  position  of  the  preceding  band  of  the  series.    This  hypo- 


POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


109 


thetical  position  was  taken  as  the  starting-point  of  the  corresponding 
absorption  series,  the  hypothetical  positions  of  the  subsequent  mem- 
bers being  found  by  addition  of  the  weighted  average  for  the  observed 
interval    of  that  series. 

By  reference  to  figure  73  and  to  tables  35  and  37,  the  reader  can  note 
the  general  agreement  between  observed  and  calculated  positions;  also 
the  occasional  discrepancies.  In  the  spectra  of  uranyl  ammonium 
chloride  and  uranyl  rubidium  chloride  for  example,  the  B^  and  A^ 
series  are  spaced  at  such  an  interval  that  aw  and  hw  can  not  coincide, 
as  will  be  seen  from  figure  73.  The  observed  hwQw  bands  occupy  posi- 
tions between  the  assumed  positions  of  the  b  and  a  series,  which  tends 
to  show  that  the  ba  band  is  a  narrow  doublet.  The  fact  that  a  few  of 
the  observed  absorption  bands  do  not  appear  to  be  in  their  proper 
places  can  be  readily  explained  when  it  is  remembered  that  there  is 
suflScient  experimental  evidence  to  lead  to  the  belief  that  many  of  the 
absorption  bands  are  doublets,  consisting  of  a  strong  and  a  weak  com- 
ponent. The  breaks  in  a  few  of  the  absorption  series,  as  in  the  eg  and 
ag  series  of  the  uranyl  ammonium  chloride,  are  undoubtedly  due  to  the 
sudden  increase  in  strength  of  one  component,  accompanied  by  a 
corresponding  decrease  in  the  other  component. 

Table  35  contains  the  observed  positions  of  all  the  fluorescence  and 
absorption  bands  at  +20°,  measured  in  our  determinations  of  the 
spectra  of  the  four  salts.  Figure  73  is  a  map  of  only  the  central  portion, 
extending,  as  already  stated,  two  groups  into  the  fluorescence  on  the 
one  side  and  two  groups  into  the  absorption  on  the  other. 
Table  35. — Polarized  series  at  +20°  C. 


URANTL    POTASSIUM    CHLORIDE. 


Fluorescence. 

Green  component. 

White  component. 

C. 

D. 

E. 

A. 

B. 

C. 

E. 

A. 

1821.0 
1903.1 
1984.6 

1756.3 
1838.6 
1922.0 

1774.6 
1856.9 
1940.6 

1788.9 
1871.2 
1955.2 

1770.9 
1853.5 
1937.5 

1958.0 

1804.2 
1887.1 
1970.1 

1827.2 
1909.6 
1992.0 

Absorption. 

Green  component. 

White  component. 

c. 

d. 

e. 

a. 

ba. 

c. 

Ci 

1985.7 
2054.2 
2125.4 

2004:  A 
2073.8 
2145.5 

2024.7 
2094.7 
2165.9 

2036.7 
2106.7 

1968.1 
2039.6 
2111.0 
2179.1 

1994.4 
2064.8 
2134.9 

2019.8 
2090.7 
2160.8 

2287.8 
2359.0 

2247.7 

2398.1 

2602.4 
2673.8 
?74.'^  .I 

2624.0 
2695  4 



2635.0 

1 

no 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  35. — Polarized  series  at  20°  C. — continued. 

URANYL   AMMONIUM    CHLORIDE. 


Fluorescence. 

Green  component. 

White  component. 

C. 

D. 

E. 

A. 

B. 

C. 

E. 

A. 

1742.1 
1824.0 
1907.0 
1990.0 

1756.4 
1840.3 
1923.6 

1775.8 
1857.6 
1941.6 

1790.0 
1874.1 
1957.8 

'isoi!^" 

1886.8 
1970.6 

1748.4 
1829.6 
1912.9 

1770.9 
1853.8 
1937.0 

1959.0 

Absorption. 

Green  component. 

White  component. 

c. 

d. 

e. 

a. 

ha. 

c. 

e. 

1988.5 
2057.3 
2128.1 

2007.9 
2077.3 
2146.9 
2218.1 
2289.7 
2360.8 
2431.4 
2500.8 
2571.4 

2026.5 
2098.1 
2169.8 
2240.1 
2313.2 
2383.3 
2455.8 
2525.9 

2039.9 
2110.9 
2182.3 
2256.8 
2327.7 
2399.2 

1970.5 
2042.6 
2114.1 
2185.0 

1999.8 
2070.2 
2140.5 

2022  A 
2094.7 
2166.0 

2311.8 
2381.8 

2623.3 

URANTL  RUBIDIUM   CHLORIDE. 


Fluorescence. 

Green  component. 

White  component. 

C. 

D. 

E. 

A. 

B. 

C. 

E. 

A. 

1739.1 
1822.7 
1905.0 
1986.9 

1757.6 
1840.9 
1923.9 

1781.9 
1865.3 
1948.8 

1750.6 
1832.4 
1916.4 

1774.7 
1858.0 
1941.6 

1793.6 
1875.5 
1959.5 

1973.7 
1956.9 

1808.8 
1891.1 
1975.3 

Absorption. 

Green  component. 

White  component. 

c. 

d. 

e. 

a. 

ah. 

c. 

e. 

1991.2 
2059.3 
2130.4 

2008.4 
2079.4 
2151.0 

2030.0 
2101.7 

2040.4 
2111.5 

1973.7 
2043.8 
2114.9 

2148.8 
2253.8 

1999.2 
2069.1 
2140.2 
2209.5 

2024.3 
2094.7 
2165.9 

2294.1 
2364.1 
2434.9 
2507.5 
2579.3 





2629.5 



2590.7 

2677.4 



POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


Ill 


T 

ABLE  35. 

— Polarized  series  at  20°  C. — continued. 

URANTL   CESIUM   CHLORIDE. 

Fluorescence. 

Green  component. 

White  component.                   1 

B. 

C. 

D. 

E. 

A. 

B. 

C. 

E. 

A. 

1761.2 
1843.3 
1927.5 

1778.1 
1860.8 
1944.4 

1789.9 
1873.7 
1956.2 

1729.8 
1812.3 
1894.3 
1978.0 

1751.3 
1835.2 
1917.9 
2000.4 

1775.6 
1858.0 
1941.4 

1793.4 
1875.8 
1958.1 

1807.3 
1891.1 
1973 . 6 

1827.2 
1909.9 
1992.0 

Absorption. 

Gref 

;n  compor 

lent. 

r 
White  component. 

b. 

c. 

d. 

e. 

a. 

h. 

c. 

e. 

a. 

1973.9 
2045.6 

2116.4 

2187.0 

1991.6 
/2057.6 
\2065.7 
/2127.9 
\2133.1 
/2198.3 
\2202.2 

2007.4 
2076.4 

2028.6 
2098.6 

2036.4 
2107.6 

1978.2 
2049.0 

2002.8 
2072.1 
2140.9 
2212.9 

2024.5 
2094.9 
2164.9 
2235.6 

2037.1 
2107.9 
2179.1 

2145.2 

2170.1 

2179.1 



2214.6 

2284.1 
2355.4 
2426.9 
2496.3 
2567.4 
2637.1 

2467.9 
2538.7 

2624.0 
2696.1 

2602.1 
2673.8 

THE  EFFECT  OF  LOW  TEMPERATURES  ON  THE  RESOLUTION  AND 
POSITION  ,.OFj  THE  |BANDS. 

It  has  been  shown  in  Chapter  V  that  low  temperature  tends  to 
narrow  all  the  bands  in  the  spectra  of  the  double  chlorides,  to  resolve 
them  into  doublets,  and  to  produce  certain  shifts  in  their  position. 
These  temperature  shifts  were  explained  by  assuming  that  the  bands 
at  +20°  are  close  overlapping  doublets,  the  stronger  components  of 
which  are  weakened  by  lowering  the  temperature,  while  the  weaker 
components  are  strengthened.  Such  shifts  occur  in  all  of  the  polarized 
spectra  here  under  consideration  and  the  same  explanation  is  appli- 
cable.   They  will  be  considered  in  detail  in  a  later  paragraph. 

In  table  36  are  recorded  the  observed  positions  of  the  fluorescence 
and  absorption  bands  in  the  two  polarized  components  at  —185°. 

Figure  74,  like  figure  73,  is  a  map  of  four  contiguous  groups,  two  of 
fluorescence  and  two  of  absorption,  inserted  to  facilitate  the  compari- 
son of  the  green  and  white  components  as  regards  the  location  of  the 
bands.  Since  the  arrangement  repeats  itself  from  group  to  group,  it 
is  unnecessary  to  include  the  outlying  regions  toward  the  red  and 
toward  the  violet. 


112 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Table  36. — Polarized  series  at  -186°  C. 

URANYL   POTASSIUM    CHLORIDE. 


Fluorescence. 

Green  component. 

White  component. 

C. 

D. 

E. 

A. 

A'. 

B. 

C. 

E. 

A. 

1738.4 
1820.5 
1903.3 
1985.7 

1785.4 
1868.8 
1953.5 

1797.9 
1881.7 
1966.6 

1891.4 
1975.5 

1741.3 
1826.2 
1911.7 
1996.0 

1771.9 
1854.9 
1938.5 

1786.4 
1870.9 
1954.7 

1842.3 
1926.0 

1858.1 
1940.8 

Absorption. 

Green  component. 

White  component. 

c. 

d\ 

d. 

d'\ 

c. 

b. 

e. 

a. 

2010.5 

2000.4 
2067.8 
2137.7 
'2207.5 

2114.2 
2184.8 
2257.8 

2021.0 
2092.7 
2164.0 

2041.2 
2112.2 
2182.6 
2252.7 

2058.0 
2128.1 
2199.3 

2076.6 
2146.8 
2218.7 
2289.9 

2086.4 
2157.5 
2228.8 
2301.5 
2371 . 1 
2440.8 
2512.3 

2152.9 
2222.2 

2541.9 

2485.7 



e. 

e'. 

a. 

c\ 

2024.3 
2094.2 
2164.5 

2028.4 
2099.1 
2169.7 
2241.4 

2036.2 
2106.6 
2177.8 
2248.5 

2124.0 
2193.5 

2384.9 

2525  3 

25.^2.9 

URANYL   AMMONIUM 

CHLORIDE. 

Fluorescence. 

Green  component. 

White  component. 

C. 

C. 

D. 

E. 

A. 

B'. 

B. 

C. 

C\ 

1738.5 
1821.2 
1905.1 
1988.9 

1744.6 
1828.0 
1911.7 
1994.8 

1751.2 
1835.5 
1919.7 
2004.2 

1777.5 
1861.6 
1946.7 

1843.5 
1928.2 
2012.5 

1857.7 
1941.0 
2023.5 

1783.6 
1868.1 
1952.4 

1803.8 
1888.4 
1972.9 

1810.1 
1894.1 
1978.2 

Absorption. 

Green  component. 

White  component. 

c. 

d. 

e. 

a. 

a'. 

b. 

c. 

e. 

e'. 

2023.6 
2094.9 

2037.9 
2108.8 

2044.2 
2115.5 

2018.8 

2030.3 

/2063.0 
\2066.0 
/2135.5 
\2138.4 
/2205.1 
\22O8.7 
/2276.6 
\2279.5 

2085.8 

2049.4 
2121.2 
2192.0 
2263.8 
2334.8 

2077.6 
2148.6 
2217.8 
2287.8 
2359.0 

2233.1* 
2302.8 

2102.2 
2174.0 

2156.6 

2166.6 

2181.1 



2227.9 

2238.6 

2249.7 



2321.5 



POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


113 


Table  36. — Polarized  series  at  —185°  C. — continued. 

URANYL   RUBIDIUM   CHLORIDE. 


Fluorescence. 

Green  component. 

White  component. 

B. 

C. 

D. 

A. 

B. 

C. 

A. 

"  i864!7  ' 
1887.9 
1971.4 

1746.4 
1828.8 
1912.0 
1994.2 

1755.0 
1837.2 
1920.9 
2004.6 

1845.7 
1929.9 
2013.7 

1874.8 
1958.9 

1812.4 
1895.9 
1979.0 

1879.2 
1962.3 

Absorption. 

Green  coi 

nponent. 

White  component. 

6. 

c'. 

c. 

d". 

b. 

c. 

e. 

^. 

2045.0 
2115.5 
2187.2 

2066.1 
2136.8 
2207.5 
2279.5 
2350.7 
2420.5 
2491.3 
2561.5 

2004.8 
2076.2 
2146.6 
2216.3 

2030.5 
2100.2 
2172.0 

2238! i' 
2309.5 
2378.0 
2451.0 



2050.4 
2122.2 
2192.0 
2263.0 
2333.7 

2200.7 
2272.7 

2223.0 
2294.1 
2362.9 
2435.5 
2504.4 
2576.3 

2359.0 



2485.1 

2541.3 

2478.3 
2548.4 

2498.1 
2570.0 

2526.5 

d. 

d\ 

a'. 

a. 

2016.7 
2085.5 
2159.8 
2229.2 

2035.8 
2108.4 

2233.9 
2305.0 
2375.0 
2446.2 
2515.4 

2246.7 

2254.3 
2325.8 

2369.1 

2391.6 
2463.1 
2532.9 

2537.4 

URANYL 

CESIUM   CHLORIDE. 

Fluorescence. 

Green  component. 

White  component. 

C. 

D'. 

D. 

E. 

A. 

B. 

C. 

E. 

A. 

1750.7 
1834.2 
1916.8 
1997.4 

1794.1 
1878.0 
1962.1 

" 1816.6 ' 
1899.8 
1983.6 

1757.8 
1841.3 
1924.6 
2007.8 

1947.0 

1794.9 
1879.0 
1963.1 

1847.1 
1930.5 
2013.7 

1852.3 
1935.8 
2019.0 

1866.7 
1950.3 

114 


FLUORESCENCE    OF   THE    URANYL   SALTS. 

Table  36. — Polarized  series  at  —185"  C. — continued. 
URANYL  CiESiuM  CHLORIDE — Continued. 


^ 


Absorption. 

Green  component. 

White  component. 

b. 

b'. 

c' 

c. 

c". 

ba. 

c. 

c. 

2050.8 
2122.2 
2192.7 

2262.4 

2333.7 

2403.8 

2475.2 

2545.2 
2615.7 

2126.8 

2267.1 
2337.5 
2409.6 

2482.6 

"262i!2 
2695.1 

2063.6 
2134.5 
2204  A 

2274.8 

2345.8 

2489.4 

2561.5 
2631.6 
2701.2 

2009.6 
2081.4 
2152.9 

2222.8 

2294.1 

2366.3 

2435.2 
2505.0 

2033.4 
2103.9 
2174.9 

2245.0 

2317.0 

2386.0 

2458.2 
2529.1 

2140.9 

2211.9 

/2280.5 

\2284.7 

2354.0 

/2422.5 

\2426.6 

/2492.5 

\2495.6 

2566 . 1 

2635.4 

2707.1 

'22i8!5' 

12289.4 

2359.0 

|2431.3 

Woo.  6 

2572.7 
2644.8 

2050.8 
2122.2 

2192.8 

2262.4 

2333.9 

2404.1 

2646.9 

d'. 

d. 

e'. 

e. 

a. 

'2227.5" 
2299.1 
2368.8 
2441.4 
2510.0 

2021.0 
2091.6 
2163.1 
2233.4 

'2378^7" 
2449.2 
2520.2 

'2238!6" 
2310.5 
2382.7 

"2524!6' 

2035.8 
2107.0 
2178.2 

232i.3 
2394.1 
2464.9 
2534.2 

2044.6 
2115.1 
2184.8 
2257.8 
2327.7 
2400.4 
2467.9 
2541.3 

As  in  these  spectra  at  +20°,  so  at  —185°  we  find  the  D  bands  only 
in  the  green  component,  the  B  bands  chiefly  in  the  white  component. 

In  the  white  component,  at  both  temperatures,  B,  C,  and  A  He 
toward  the  violet,  E  toward  the  red.  At  — 185°,  B  is  doubled  in  the 
uranyl  ammonium  chloride,  D  in  the  uranyl  chloride. 

To  aid  in  the  direct  comparison  of  the  spectra  at  the  two  tempera- 
tures, they  are  plotted  together  in  figure  75,  in  which  diagram  may  be 
seen  the  direction  of  the  shift  for  each  series  of  the  two  components. 

The  shift  is  nearly  always  toward  the  violet,  the  only  exceptions 
being  the  Ag  and  ag  series  and  possibly  the  A^  series  in  uranyl  potas- 
sium chloride  (see  fig.  74),  the  eg  and  eg  series  of  uranyl  ammonium 
chloride  and  the  Ay  series  of  the  latter  salt.  The  change  is  greatest 
in  uranyl  caesium  chloride  and  least  in  the  potassium  double  chloride. 

In  general  the  fluorescence  bands  shift  in  the  same  direction  and 
by  the  same  amount  as  the  related  absorption  bands,  but  there  are 
some  puzzling  exceptions  to  this  rule  to  be  considered  in  a  following 
section. 

The  increased  resolution  of  the  spectra  upon  cooling  shows  itself  in 
the  doubling  of  many  bands  which  appear  single  at  +20°,  an  effect 
particularly  noticeable  in  the  absorption  spectra.  (See  plate  1,  c.) 
Thus  the  Cg  series  of  the  potassium  salt  tends  to  double  at  2,058.0 


POLARIZED  SPECTRA  OF  DOUBLE  CHLORIDES. 


115 


and  becomes  clearly  double  at  2,128.1  and  2,199.3.  The  dy  and  eg  series 
of  the  same  salt  are  doubled  and  the  ha  series  of  +20°,  which  was 
assumed  from  the  relations  of  the  spectrum  to  be  an  unresolved  doub- 
let, is  separated  into  a  hw  and  an  aw  series  at  -185°.  Other  examples 
of  doubling  may  be  noted  in  the  case  of  Cg,  Cg,  ag,  and  B^  of  uranyl 
ammonium  chloride,  ag,  aw,  and  bw  of  the  rubidium  salt,  and  hw,  Dg,  and 
dg  of  the  caesium  salt. 


leloo 


I9|00 


20|00 


2l|00 


■185* 


aREBN 


URAMYt   POTASSIUM  CHLORIDE 
C  C  C 

'  ht?  i  f  if  I  fif  r 
1 1 1 II I II 


EA  B 

-U-i- 


WHITB 


E   A      7 


E  A 

I    I 


URANYL  AMMONIUM  CHLORIDE 

C  C  C 

QREEN  (H      I    E  A  Cl      ?  E  A 

ll      I     II ll      I    I    I 


e  ab    c       e  a  b   c 


dea       c    dea      c 
« Ml       I 


nr 


^\ 


,xB?  ^^     ^.       e'  b       c      e    b 

E       ?i  E       ■■      ' 


T II 


QREEN 


URAMYL  RUBIDIUM  CHLORIDE 

f  ll  t;  i '  ;r 


fff4-H 


d.     aJb     c    d    ah    c 


\ 


WHITE 


II 


e     b 


e     b 


URAMYL    CAESIUM   CHLORIDjE 
C  C 


GREEN 


iLil 


iLll 


c    d  e  ab    c    d  e  ab 


I    A      ■ 

I      I       I 


E    A 


I  7   I 


e  ba     c     e  ha, 
i    II 


rr 


leloo 


zoloo 


2l|0O 


FiQ.  74. — Polarized  bands  of  fluorescence  and  absorption;  four  contiguous  groups  showing  the 
relation  between  the  green  and  white  components  at  —185°.  Dotted  lines  show  computed 
positions  of  absorption  bands;  solid  lines  above  the  base  indicate  fluorescence,  below  the 
base  absorption. 

ON  THE  FREQUENCY  INTERVALS  OF  FLUORESCENCE  AND  ABSORPTION. 

During  the  preliminary  study  of  the  fluorescence  and  absorption  of 
uranyl  ammonium  chloride  described  in  Chapter  V,  the  symmetry  of 
the  spectrum  was  such  as  to  lead  to  the  suspicion  that  the  various 
homologous  series  would  be  found  to  have  the  same  constant-frequency 
interval.  The  final  tabulation  of  results,  however,  after  many  redeter- 
minations of  what  seemed  to  be  discordant  values,  showed  that  while 
the  departures  from  uniformity  were  in  general  scarcely  larger  than  the 
errors  of  observation,  they  were  to  some  extent  systematic  and  indi- 


116 


FLUORESCENCE   OF  THE    URANYL   SALTS. 


cated  slightly  different  values  for  the  various  series.  The  C  bands  in 
particular,  which  were  a  composite  of  what  in  these  later  studies  we 
have  designated  as  Cy  and  C^  of  the  polarized  spectrum,  were  found 
to  have  an  unquestionably  smaller  interval  than  the  other  series  of  the 
group. 

It  will  be  seen  from  table  37  that  this  is  true  for  both  Cg  and  Cw  in 
the  case  of  all  four  salts  at  +20°  and  that  with  the  possible  exception 
of  A^,  which  is  an  exceedingly  feeble  component,  visible  only  in  two 
of  the  salts  and  very  difficult  of  determination;  all  other  series  are  very 


isloo 

1               WIOO              1              20|00              1 

2l|00 

CREEII+20' 

URAHYL   POTASSIUM    CHLORIDE 

e  Cb   c 

OREEM-.85-      1        II    1     .        1        1      1    1     .       i       1        1    1      1       1        1     1      1     1 

WHITE  4-20' 1 

f 

[  r  t  TtrUJ'lJJ 

nil  II 

e    b(v    c 

WH.TE-.85H       1          1      1       1       1          II       1      i          i       1         1          1       1         II 

GREEN  420" 

URANYL   AMMONIUM    CHLORIdI         '        "        ' 
CDEA          CDEA 

MM          MM         c    cL   e  (L  c    cb 

1   II   1 

e  a.  c 

oaEEH^es"     ,1111 1     1   1    1     1     1   1    1  1 

WHITE  ♦■20*| 

?      r        ?      9      f     AB      1     II   II     II 
11         \        \       \      W        c     e   ba.      c 

1  II   1 

e  hcb 

WHITE -lesil 

1        1        II        1        1        II      1       1      1        1 

\  1 

QREEII+20' 

Mill 

URANYL   RUBIDIUM     CHLORIDE 
C      p       EA          C      D       EA 

1            II         1     1       II    ,     c    rf    ea   c    d 

1  1 

ect   c 

GREEN -185*1 

1     1     Ml      1     1 

II  1 

B 
WHITE  4-20°    1 

flirt  nrl'Ji'c 

II    1 

e    ab 

».m...,5-  II           III          II     1       1     1      1       1     1      1 

B 
flREEN+20'l 

URANYL    CAESIUM    CHLORIDE 

II     II     1     MM     b    c    d    eab  c    d 

1   1 

eab  c 

GREEN -185' 

III  II      III  II     1  1  lllllll 

mill 

B 
WHITE  420°    1 

f  M 

r  9  f  A    1  1  III  II 

1       \     \     b      c     e  ab     c 

1  mil 

eab 

WHITE-185' 

1  1  1  1  1  1  1  1   1  1  III 

1  II 

wjoo 

Mill 

1          i»loo         1         mIoo         1 

1  1 

2l|0O 

FiQ.  75. 

nearly  of  the  same  interval,  not  only  in  the  same  salt  but  in  all  the  salts. 
When,  however,  we  make  further  averages  of  the  average  intervals  from 
table  37,  taking  the  mean  of  all  green  components  of  fluorescence, 
'then  of  all  white  components,  for  each  salt  separately,  and  do  the  same 
for  the  absorption  intervals,  we  find  an  approach  to  systematic  arrange- 
ment which  is  suggestive  if  not  altogether  conclusive.  (See  table  37.) 
Both  components  of  the  fluorescence  spectrum  show  an  average 
interval  in  the  inverse  order  of  the  molecular  weights,  and  while  the 
absorption  series  do  not  give  so  decisive  an  indication  the  salts  of  lesser 


POLARIZED    SPECTRA   OF   DOUBLE    CHLORIDES. 


117 


molecular  weight,  NH4  and  K  show  again  a  longer  interval  than  do  Rb 
and  Cs.  Averaging  by  series  affords  no  such  direct  indication  as  to 
differences  of  interval,  as  will  appear  from  table  38. 

It  will  be  noted  that  while  the  averages  for  the  green  and  white  com- 
ponents of  fluorescence  are  in  very  close  agreement  at  +20°  and  also 
at  — 185°,  there  is  a  difference  of  about  0.5  between  the  averages  for 
+20°  and  those  for  —185°;  also  that  the  interval  is  greater  for  each 
individual  series  at  —185°  than  at  +20°,  with  the  single  exception  of 
ew.  This  difference  does  not  appear,  however,  in  the  case  of  the  absorp- 
tion intervals. 

Table  37. — Average  frequency  intervals,  -\-W  C.  and  -186°  C. 


Series. 


Bo. 
Do- 

Ag. 


Series. 


Fluorescence  series. 


Green  component. 


K 


81.9 
83.0 
83.2 
83.4 


NH4       Rb         Cs 


82.8 
83.5 
83.3 

83.8 


82.2 
83.1 
83.5 
83.2 


82.9 
82.6 
83.3 
83.3 
82.9 


White  component. 


Series. 


o«i. . 


83.0 
82.1 


83.6 


NH4       Rb        Cs 


83.4 
82.9 


83.1 


83.6 
83.3 


83.5 
82.9 


Absorption  series. 


K        NH4       Rb 


71.3 
71.1 
70.8 
70.7 


70.7 
70.5 
70.8 
71.5 


71.2 
70.2 
71.7 
71.1 


Cs 


70.5 
70.6 
70.5 
71.0 
70.8 


Series. 


Cw 


71.5 
71.3 


70.4 
71.5 


NH4 


71.3 
70.3 


71.7 
71.3 


Rb 


70.4 
70.0 


70.8 
70.4 


82.9 
82.8 


83.1 
82.4 


Cs 


70.8 
70.5 


70.4 
71.4 


Average  frequency  intervals,  -186 

°C. 

Fluorescence  series. 

Green  component. 

White  component. 

Series. 

K 

NH4 

Rb 

Cs 

Series. 

K 

NH4 

Rb 

Cs 

C,.... 
A„.... 

84.0 
82.5 
83.7 
83.3 
84.1 

83.4' 

84.4 
83.2 
84.4 

83.4 
82.6 
83.9 

'84!i' 

82.2" 
83.3 

83.6 
84.1 

B„... 

84.1 
84.8 

84.1 
84.4 

83.2 
83.9 

83.6 
83.3 

Au,... 

83.0 
84.0 

83.1 
84.1 

83.1 

Absorption  series. 

Series. 

K 

NH4 

Rb 

Cs 

Series. 

K 

NH4 

Rb 

Cs 

b„ 

70.9 
70.7 
71.3 

'76.6' 

70.5 
70.8 
71.4 
71.0 
71.1 

71.3 
69.8 

71.3 
70.6 

70.8 
70.3 

70.6 
70.7 

Z::::. 

^0 

ag 

71.5 
70.3 

71.8 
71.0 

70.9 
71.1 
71.5 
70.9 

e„... 

71.4 
70.4 

70.7 

71.1 

70.9 
70.6 

118 


FLUORESCENCE    OF   THE    URANYL   SALTS. 

Table  37. — Average  frequency  intervals,  +20°  C.  and  185°  C. — continued. 
General  averages  of  intervals  (by  salts). 


Fluorescence. 

NH4. 

K. 

Rb. 

Cs. 

Green  +20°  and  -185"... 
White  +20°  and  -185°... 

All  fluorescence 

83.60 

83.78 

83.25 
83.43 

83.25 

83.42 

83.19 
83.16 

83.69 

83.34 

83.33 

83.17 

Absorption. 

Green  +20°  and  -185°... 
White  +20°  and  -185°... 

All  absorption 

70.99 
71.02 

71.07 
70.96 

70.96 
70.55 

70.74 
70.70 

71.00 

71.01 

70.75 

70.72 

Table  38. — General  averages  of  intervals  {by  series 

). 

Fluoiescence. 

Series. 

Green. 

Av. 

Series. 

White. 

Av. 

+20° 

-185° 

+20° 

-185° 

Eg.... 
Be 

83.33 

83.37 
83.70 

84.18 
83.83 
82.68 

83.35 
83.70 
83.72 
83.53 
82.53 

Ew... 
Bw... 
Aw... 
Dw. 

83.37 
83.23 
82.80 

83.05 
83.75 
83.73 

83.17 
83.49 
83.74 

Ag.... 
Dg.... 
Cg.... 

Av. . . . 

83.26 
83.23 
82.38 

Cw... 

Av. . .  . 

82.78 

84.10 

83.44 

83.05 

83.54 

83.37 

83.05 

83.66 

83.36 

Absorption. 

+20° 

-185° 

Av. 

+20° 

-185° 

Av. 

eg 

ba 

71.07 

71.40 

71.23 

ey, 

bu>.... 
a„ 

70.82 
71.00 
70.90 

71.02 
71.00 
70.70 

70.90 
71.00 
70.80 

% 

dg 

^0 

Av.... 

71.02 
70.58 
70.95 

70.90 
71.02 
70.98 

70.96 
70.75 
70.96 

Cw 

Av. . .  . 

70.50 

70.35 

70.42 

70.90 

71.07 

70.97 

70.81 

70.77 

70.78 

On  the  other  hand,  differences  so  large  are  not  to  be  regarded  as 
errors  of  observation,  it  being  possible  to  determine  the  average  inter- 
val of  any  series,  excepting  possibly  Ag  and  A^,  which  are  very  weak  and 
rather  vague,  within  about  0.2.  It  does  not  follow,  however,  that  the 
bands  are  really  thus  irregularly  placed.  The  discrepancies  are  due 
rather  to  the  fact  that  resolution  is  not  equally  complete  in  all  portions 
of  the  spectrum  and  that  on  cooling  the  crystal  structure  was  more  or 
less  disturbed  and  the  polarization  always  much  less  complete.  The 
anomalous  values  above  84  frequently  observed  at  —185°  (see  table 
37)  are  probably  due  to  varying  components  of  the  opposite  polar- 
ization superimposed  on  the  bands  in  question  and  producing  a  false 


POLARIZED    SPECTRA    OF   DOUBLE    CHLORIDES. 


119 


shift.  Thus,  for  example,  the  position  of  C^  would  be  modified  by  the 
presence  of  the  overlapping  of  D^  or  C^;  D^  by  Cg,  etc.  In  short*,  it  is 
probable  that  if  observations  could  be  had  on  crystals  which  at  — 185° 
preserved  their  structure,  the  difference  in  interval  between  +20°  and 
—  185°  would  disappear. 

THE  INFLUENCE  OF  MOLECULAR  WEIGHT  UPON  THE  POSITION  OF  BANDS. 

While  some  doubt  may  be  felt  as  to  the  validity  of  the  suggestion, 
based  upon  the  averages  presented  in  the  foregoing  paragraphs,  that 
there  is  a  relation  between  frequency  intervals  and  the  molecular 
weight,  there  can  be  no  question  as  regards  the  influence  of  molecular 
weight  upon  the  position  of  the  bands. 


I       i        1 1 1 — 1 

.60/*     .55  .<6       .50^          .45 /^^            .40 ><^ 

^   NH,       1    1     1    i    !    : 

^-  Rb       III;.;. 

CS      I      1      1       1     ! 

K          1     1     1    i    i             1 

^„  NH,    1     1     1     11! 

R^     1     1     II!! 

Cs          ill 

K           1     1     1     i    1 

^   NH.    1     1     1     1         1    : 

"  Rb     1     1     1     1    i    !    i 

Cs      1      1     1      1     1     1     1 

^              III;::       !    5 

^  NH,    1    1    1   •;   :   1   ;   !   ;   :   : 

Rb    1    1    1    1   ;   !      ;   !   :   ! 

Cs     1    1    1    ;::::::; 

K       1     1     1     i    :    : 

NH,     1    1    1     ;    1    ;       ;    ; 

"-  Rb     III;:; 

Cs     1   1    1   ;   ;   ;   i 

y^                   1     1     1     i    i    • 

e„  NH,    1   1   1   i   ;   ;   ;   ;   I 

Rb       1     1     1     1    : 

Cs      1     1     1     ;    i 

•^     1   1   1   ;   1 

a,,,   HH^              1    1    1    1    1    :    ; 

Rb       1   1   ;   ; 

Cs       1     1     1    :    1    ! 

K                1    :    :    : 

«H-  NH^              1    :    S 

: 

Rb      1    1    1    :    :   ! 

Cs      1    1    1    :    ;   ! 

J 

«7  .  '.«  .  '?  .  ^P  .  ^\    .  ^}   .   ^»  -  '^   .  V  1 

Fig.  76. 


If  we  select  a  typical  region  in  the  spectrum  and  arrange  the  bands 
belonging  to  a  single  group  as  in  table  39,  we  find  a  general  drift  of  the 
various  bands  toward  the  violet  as  we  pass  from  salt  to  salt  in  the 
order  K,  NH4,  Rb,  Cs. 


120 


FLUORESCENCE    OF   THE    URANYL    SALTS. 


The  same  drift  occurs  quite  systematically  throughout  the  entire 
fluorescence  and  absorption  spectrum,  as  may  be  seen  from  figure  76. 
In  this  chart  such  of  the  fluorescence  and  absorption  series  as  are 
present  in  all  four  salts  at  +20°  are  plotted  on  the  frequency  scale. 
The  solid  lines  represent  observed  fluorescence  bands;  the  dotted  lines 
represent  observed  absorption  bands;  no  hypothetical  values  are 
indicated.    The  order  of  the  salts  is  the  same  as  in  table  39  and  follows 

Table  39. 


Green  polarization,  185°. 

White  polarization,  185<=*. 

Cg. 

Dg. 

Eg. 

Ag. 

Bw. 

Cw. 

Ew. 

Aw. 

K 

NH4... 
Rb.... 
Cs.... 

1903.3 
1911.7 
1912.0 
1916.8 

1842.3 
1843.5 
1845.7 
1852.3 

1940.8 
1941.0 

igso^s' 

1868.8 
1868.1 
1874.8 
1878.5 

1891.4 
1894.1 
1895.9 
1899.8 

1911.7 
1919.7 
1920.9 
1924.6 

1854.9 

1870.9 

"i862!5' 

1879.2 
1879.9 

that  given  by  A.  E.  Tutton  in  his  Treatise  on  Crystalline  Structure  and 
Chemical  Constitution  (London,  1916).  He  found  for  both  single  and 
double  salts  of  the  alkali  metals  that  several  of  their  optical  properties, 
such  as  refractive  index,  etc.,  follow  the  order  of  the  molecular  weights, 
but  that  in  the  ammonium  salts  the  NH4  radical  often  acts  as  if  it  were 
much  heavier  than  the  combined  weights  of  its  components  would 
indicate,  so  that  its  position  is  quite  close  to  rubidium  and  sometimes 
on  the  side  toward  caesium.  It  will  be  observed  that  there  are  several 
examples  of  this  in  figure  76,  particularly  in  the  case  of  the  Cg  series. 

SUMMARY. 

(1)  The  four  double  chlorides,  uranyl  ammonium  chloride,  uranyl 
potassium  chloride,  uranyl  rubidium  chloride,  and  uranyl  caesium  chlo- 
ride, crystallize  in  the  triclinic  system.  The  crystals  are  pleochroic 
and  their  fluorescence  spectra  and  absorption  spectra  are  polarized. 

(2)  The  spectra  differ  from  those  of  other  uranyl  compounds  thus 
far  examined  in  that  both  in  the  fluorescence  and  absorption  regions 
each  band  is  resolved  at  +20°  C.  into  a  group  of  five  bands  forming 
homologous  series  of  constant  frequency  interval. 

(3)  The  structure  of  the  fluorescence  spectrum  is  essentially  the 
same  in  the  different  salts,  the  spacing  of  the  bands  of  each  group 
repeating  itself  in  the  successive  groups,  excepting  in  the  reversing 
region,  the  appearance  of  which  is  modified  by  the  overlapping  of 
fluorescence  and  absorption. 

(4)  Each  of  the  five  bands  which  constitute  a  group  is  a  doublet,  the 
two  components  of  which  are  polarized  at  right  angles  to  one  another. 

(5)  The  frequency  interval  is  the  same  or  nearly  the  same  for  each 
series  in  a  given  salt. 


POLARIZED  SPECTRA  OF  DOUBLE  CHLORIDES.  121 

(6)  Variations  in  the  average  interval  for  the  four  salts  are  scarcely 
greater  than  the  errors  of  observation,  but  there  are  indications  of  a 
very  slight  decrease  of  interval  with  increase  of  molecular  weight,  and 
this  applies  alike  to  fluorescence  and  absorption  series. 

(7)  The  position,  in  the  spectrum,  of  a  given  band  varies  slightly  but 
systematically  with  the  molecular  weight  of  the  salt.  The  order  of 
diminishing  wave-lengths  is  K,  NH4,  Rb,  Cs;  the  shift  from  K  to  Cs 
being  of  the  order  of  5  A.  u.  This  shift  is  in  the  same  direction — from 
red  toward  violet — for  all  the  homologous  series  and  of  the  same  size 
within  the  errors  of  observation. 

(8)  Cooling  to  the  temperature  of  hquid  air  produces  the  usual 
narrowing  of  bands,  apparent  shifts  of  position,  and  apparent  changes 
of  interval,  all  of  which  changes  are  explained  by  the  relative  enhance- 
ment or  diminution  of  components  of  the  bands. 


VII.    THE  NITRATES  AND  PHOSPHATES;    INFLUENCE  OF 
WATER  OF  CRYSTALLIZATION  AND  OF  CRYSTAL  FORM. 

I.  URANYL  NITRATE  AND  EFFECT  OF  WATER  OF  CRYSTALLIZATION. 

The  spectra  of  the  different  uranyl  salts  are  so  similar  in  their  general 
characteristics  that  we  can  scarcely  doubt  that  the  nature  of  these 
spectra  is  chiefly  determined  by  the  radical  UO2.  Apparently  the 
uranyl  radical  contains  a  group  of  electrons  whose  arrangement  is 
such  as  to  permit  of  vibrations  that  give  this  type  of  spectrum;  and 
although  UO2  is  not  stable  in  the  chemical  sense  and  must  be  com- 
bined with  some  acid  in  order  to  form  a  stable  compound,  yet  the 
effect  of  the  acid  radical  is  merely  to  modify  the  constants  of  this 
vibrating  system  in  the  UO2  radical  without  changing  the  type  of 
vibration. 

It  is  natural  to  expect  that  the  addition  of  water  of  crystallization 
would  produce  a  similar  effect,  and  it  is  our  intention  to  present  in  this 
section  of  Chapter  VII  the  results  of  a  study  of  the  influence  of  water 
of  crystallization  upon  the  fluorescence  and  absorption  spectrum  in 
the  case  of  uranyl  nitrate.  The  nitrate  is  particularly  suited  for  such 
an  investigation  because  of  the  fact  that  several  different  hydrates  are 
formed.  The  crystals  grown  from  a  water  solution  contain  6  molecules 
of  water.  In  an  acid  solution  crystals  are  formed  with  3  molecules  of 
water.  In  both  cases  crystals  may  be  obtained  which  are  large  enough 
to  permit  of  observations  being  made  with  a  single  crystal.  By  methods 
described  later,  small  crystals  containing  only  2  molecules  of  water  are 
readily  obtained.  It  is  a  matter  of  some  difficulty  to  push  the  dehy- 
dration further,  but  specimens  have  been  prepared  for  us  by  Mr. 
D.  T.  Wilber  which  we  have  reason  to  believe  are  either  anhydrous  or 
formed  of  a  mixture  of  the  anhydrous  salt  and  the  monohydrate. 

The  fluorescence  of  the  nitrate,  like  that  of  the  other  uranyl  salts, 
with  the  exception  of  the  double  chlorides,  the  resolution  of  the  bands 
of  whose  spectra  into  groups  of  five  at  +20°  has  been  described  in 
Chapter  VI,  is  unresolved  at  ordinary  temperatures.  Careful  spectro- 
photometric  measurements  of  what  appear  to  be  unresolved  bands 
reveal,  however,  indications  of  overlapping  components,  as  has  already 
been  shown  in  Chapter  III. 

At  the  temperature  of  liquid  air  the  resolution  into  narrow  bands 
characteristic  of  the  uranyl  spectra  in  general  takes  place,  and  it  is  to 
these  resolved  spectra  that  the  following  discussion  refers. 

In  the  case  of  the  hexahydrate,  wave-lengths  were  in  most  cases 
determined  photographically,  \isual  observations,  however,  were 
also  made,  although  these  could  not  be  extended  throughout  the  whole 
spectrum.  The  agreement  between  measurements  made  by  the  two 
methods  was  surprisingly  good.  In  the  case  of  weak  bands  lying  near 
122 


THE   NITRATES   AND   PHOSPHATES.  123 

to  bands  of  great  intensity  the  visual  observations  were  found  to  be 
best.  The  results  given  for  the  fluorescence  spectra  of  other  hydrates 
and  for  the  anhydrous  salt  are  based  upon  visual  observations  exclu- 
sively. 

The  Hexahydrate:  U02(N03)2-f  6H2O. 

The  hexahydrate  crystallizes  in  the  rhombic  system  with  the  axial 
ratio  a:  b:  c  =  0.6837 : 1 : 0.6088.  The  crystals  were  grown  in  the  form  of 
plates  by  using  a  water  solution  whose  depth  was  equal  to  the  thick- 
ness of  the  plate  desired.  Single  crystals  as  large  as  15  mm.  in  diameter 
were  obtained  with  relatively  little  difficulty.  All  of  the  results  here 
discussed  are  based  upon  observations  made  with  single  crystals. 

In  selecting  the  data  to  be  used  in  taking  a  final  average,  each  nega- 
tive was  carefully  studied  and  measurements  that  seemed  for  any 
reason  doubtful  were  discarded.  The  elimination  of  doubtful  observa- 
tions was  made  without  reference  to  the  agreement  or  lack  of  agree- 
ment between  the  different  measurements,  and  was,  in  fact,  completed 
before  the  measurements  of  the  different  negatives  were  compared. 
About  40  negatives  were  used,  although  the  number  for  any  one  Une 
was  rarely  more  than  10. 

The  errors  of  calibration  of  the  spectrograph  and  spectrometer  can 
hardly  exceed  1  a.  u.,  except  perhaps  in  the  extreme  red  end  of  the 
spectrum.  The  uncertainties  due  to  the  faintness  of  certain  bands,  to 
their  finite  width,  and  to  photographic  broadening  are  more  dififtcult  to 
estimate  and  undoubtedly  differ  greatly  with  the  character  of  the  band 
and  its  position  in  the  spectrum.  In  the  case  of  the  sharper  bands  of 
moderate  intensity  we  feel  that  the  averages  that  are  here  tabulated 
are  reliable  within  1  A.  u.  In  other  words,  the  reciprocal  wave-lengths 
are  accurate  to  within  about  0.02  per  cent.  For  the  faint  or  hazy  bands 
the  possible  error  is  undoubtedly  much  greater. 

Of  the  55  fluorescence  bands  observed,  46  can  be  arranged  in  9  series, 
as  tabulated  below,  the  frequency  interval  being  nearly  constant  in 
each  series.  Two  of  the  remaining  bands  have  the  same  interval,  and 
apparently  form  part  of  a  series  whose  other  members  were  too  weak 
to  detect.  The  7  bands  that  do  not  fall  in  any  series  arrangement  are 
all  extremely  weak,  and  since  in  most  cases  they  are  recorded  only  once, 
their  existence  is  subject  to  considerable  doubt.  Estimates  are  given 
in  table  40  of  the  intensities  of  the  different  bands  and  of  the  reliability 
of  the  measurements.  In  some  cases  the  series  seem  to  extend  into  the 
region  of  absorption,  and  in  such  cases  the  absorption  bands  that  seem 
to  form  part  of  the  series  are  also  given. 

The  data  for  series  B,  D,  E,  and  F,  which  are  made  up  of  the  stronger 
bands  and  those  of  medium  intensity,  are  undoubtedly  the  most  reli- 
able. The  values  of  the  average  interval  between  bands  in  these  series 
are  86.0,  85.8,  85.9,  and  86.1  respectively.    In  taking  these  averages, 


124 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


the  first  band  in  the  case  of  series  D  and  E  has  been  left  out  of  con- 
sideration on  account  of  its  relative  uncertainty.  For  the  other  series 
the  interval,  although  less  certain,  has  nearly  the  eame  value.  It  will 
be  noticed  that  there  is  nothing  to  indicate  any  change  in  the  interval 
as  we  pass  from  the  longer  to  the  shorter  waves. 

Table  40. — Series  in  the  fluorescence  spectrum  of  uranyl  nitrate  hexahydrate 
[UO,{NOz)^-\-6mO]. 


Inten- 

Relia- 

1» 

1 

Inten- 

Relia- 

P 

1 

sity.! 

bility.2 

X 

AX 

sity.! 

biUty.2 

X 

AX 

A 

v.d. 
V.  d. 

2 

1 

F  1760.1 
1846.0 

m. 
d. 

1? 
3 

F  1631.3 

1718.4 

'85!9'"* 

'87!i"" 

d. 

2 

1930.1 

84.1 

m. 

4 

1803.6 

85.2 

m. 

4 

F  2018.2 

88.1 

m. 
m. 

6 
5 

1889.6 
1976.4 

86.0 
86.8 

V.  d. 

3 

F  1689.5 

F 

d. 

4 

F  2061.9 

85.5 

d. 

3 

1775.0 

kb.k"" 

B 

m. 
m. 

4 
6 

1861.1 
1947.1 

86.1 
86.0 

m. 
m. 

4 
4 

A  2061.7 
A  2148.7 

■87!6"'" 

8tr. 

5 

F  2034.5 

87.4 

m. 

4 

A  2234.1 

85.4 

d. 

3 

A  2207.3 

86.4X2 

str. 
v.d. 

3 

1 

A  2321.0 
A  2491.9 

86.9 
85.5X2 

C 

d. 
d. 
d. 

3 

2 
2 

F  1699.0 
1785.1 
1869.0 

G 

d. 
d. 

3 

4 

F  1810.4 
1897.3 

"seii"'" 

83.9 

*86!9"" 

v.d. 

1 

1956.2 

87.2 

v.d. 

2 

1983.1 

85.8 

m. 

2 

2041.5 

85.3 

d. 

1 

A  2241.6 

86.2X3 

v.d. 
d. 

1 
3 

F  1534.9 
1621.0 

v.d. 
v.d. 

3 
2 

F  1649.7 
1737.4 

"m.'\"" 

'87!7"" 

m. 

4 

1706.8 

85.8 

H 

d. 

1 

1822.0 

84.6 

D 

str. 

5 

1792.5 

85.7 

m. 

4 

1906.7 

84.7 

str. 

6 

1877.8 

85.3 

m. 

4 

1993.4 

86.7 

str. 

6 

1963.6 

85.8 

d. 

3 

2050.0 

86.4 

i 

v.d. 
v.d. 

2 
2 

1826.0 
1911.7 

'85.'7   "" 

v.d. 
d. 

m. 

1 
2 
3 

F  1540.1 
1629.2 
1715.0 

d. 
m. 

3 
3 

F  1665.5 
1751.8 

'89!i**    ' 
85.8 

'seis'  '" 

str. 

6 

1800.0 

85.0 

d. 

3 

1837.8 

86.0 

E 

str. 
str. 

6 
6 

1886.1 
1972.5 

86.1 
86.4 

J 

m. 

4 

F  1923.1 

85.3 

str. 

6 

F  2058.5 

86.0 

d. 
d. 

4 
1 

A  2268.3 
A  2440.2 

86.3X4 
86.0X2 

m. 

5 

A  2058.6 

!  Estimated.     Str.,  strong;  m.,  medium;  d.,  dim;  v.  d.,  very  dim. 

'  The  most  reliable  results  (as  indicated  by  the  number  and  consistency  of  the  individual 
measurements,  the  appearance  of  the  negatives,  etc.)  are  marked  5;  the  least  reliable  by  1. 
•  The  unit  in  which  1/X  is  expressed  is  such  that  for  X=5,000  A.  u.     1/X  is  written  2,000. 

In  a  spectrum  consisting  of  so  many  bands,  the  occasional  repetition 
of  any  given  interval  between  bands  is  to  be  expected,  even  if  the  bands 
are  distributed  at  random.  It  is  proper  to  inquire,  therefore,  whether 
this  interval  of  about  86.0  really  occurs  more  frequently  than  would  be 
expected  for  a  random  distribution.  Data  bearing  on  this  point  are 
plotted  in  the  upper  curve  of  figure  77.  In  this  curve  horizontal  dis- 
tances indicate  the  lengths  of  different  possible  intervals  between 


THE   NITRATES   AND   PHOSPHATES. 


125 


-     U02(N03)2+6H2  0  I 


U02(N03)2  +  3H2  0 


axK^  XXX  ±xxcvi.±j        ■  U02(N03)2  +  2H2  0  I 

Sit  :^^m-ShVvUU 


bands,  while  ordinates  give  the  number  of  times  each  interval  occurred. 
The  range  of  possible  error  in  the  location  of  each  band  is  arbitrarily 
assumed  to  be  2  units.  Thus  for  a  frequency  interval  32  (abscissa)  the 
ordinate  is  10.  This  means  that  10  pairs  of  bands  were  found  for  which 
the  interval  lay  between  31  and  33. 

It  is  evident  from  the  chart  that  certain  intervals  occur  with  much 
greater  frequency  than  would  be  expected  if  the  bands  were  distributed 
at  random,  and  this  is  most  conspicuously  true  of  the  interval  86.  It 
will  be  noted  that  the  curve  also  shows  lesser  maxima  for  several  other 
frequency  intervals:  e.  g.,  8,  16,  70,  78,  and  94.  These  intervals  corre- 
spond to  the  spacing  of  the  bands  in  the  successive  groups  which  make 
up  the  spectrum. 

On  account  of  the  fact  that  large,  clear 
crystals  could  be  obtained,  the  hexahydrate 
offered  an  especially  favorable  case  for  the 
study  of  the  absorption  spectrum.  Obser- 
vations were  made  with  a  number  of  dif- 
ferent crystals  ranging  in  thickness  from  a 
few  tenths  of  a  millimeter  to  3  or  4  mm. 
The  averages  given  in  table  41  are  in  many 
cases  based  upon  15  or  more 
measurements.  In  the  case  of 
2,148.7,  for  example,  17  measurements  of 
wave-length  were  made,  of  which  3  were 
discarded  because  of  the  unsatisfactory 
character  of  the  negatives.  In  the  14 
measurements  used  in  forming  the  average, 
the  reciprocal  wave-length  ranged  from 
2,147.8  to  2,149.6,  most  of  the  values  lying 
close  to  the  average.  In  other  cases  the 
wave-length  is  much  more  uncertain.  The 
extremelyfaintbandat2,536.4,for  example, 
was  observed  on  only  two  negatives,  while  the  dim,  broad  band  at 
2,720.3  was  observed  only  once.  The  reliability  of  the  recorded  average 
has  been  estimated  in  each  case  and  is  indicated  in  the  table. 

A  study  of  the  absorption  spectrum  shows  that  an  interval  of  about 
71  between  bands  is  of  relatively  frequent  occurrence.  (See  the  lower 
curve,  fig.  77.)  In  several  instances  definite  series  exist  with  this  con- 
stant interval.  The  values  of  1/X  for  the  bands  forming  these  series  are 
given  in  table  41. 

The  two  series  e  and  /  begin  with  reversible  bands.  Thus,  the  first 
band  of  series  e,  at  1/X  =  2,058.6,  can  not  be  distinguished  in  position 
from  the  last  band,  1/X  =  2,058.5,  of  the  fluorescence  series  E,  while  the 
first  band,  1/X  =  2,061.9,  of  series/  is  coincident  with  the  band  2,061.7  of 


U02(;^03)2+6H0 
ABSORPTION 


Fig.  77. — Frequency  of  occurrence 
of  different  intervals  between 
bands.  Abscissae  show  the  in- 
tervals (1  divi3ion=10) ;  ordi- 
nates  show  the  number  of  times 
the  interval  occurs  (1  division 
=  10). 


126 


FLUORESCENCE    OF  THE    URANYL   SALTS. 


Table  41. — Series  in 

the  absorption  spectrum  of  uranyl  nitrate  hexahydrate 

[UO^{NOz)2^-6HiO]. 

Series. 

Inten- 
sity. 

Relia- 
bility. 

1 
X 

1 
AX 

Series. 

Inten- 
sity. 

Relia- 
bility. 

1 
X 

1 
AX 

c 

e 

f 

V.  d. 

str. 

d. 

V.  d. 
d. 
d. 

str. 
m. 
str. 
str. 

str. 

m. 
str. 

m. 
d. 

d. 
m. 

str. 
m. 

2 
4 
5 

4 
2 
4 
3 
3 
3 
3 

6 
6 
4 
4 

4 

4 
4 
5 
4 

2127.2 
2200.4 
2272.3 
[2053.41 
2125.0 
2196.8 
2268.3 
2340.4 
2412.0 
2484.1 
2555.3 

[2058.5] 
2058.6 
2131.2 
2203.8 

2277.8 

[2061.9] 
2061.7 
2134.1 
2207.3 

"73.'2' 
71.9 

71.6 
71.8 
71.5 
72.1 
71.6 
72.1 
71.2 

'72!6' 
72.6 
74.0 

72.4 
73.2 

h 

8 

d' 

m. 
str. 
str. 

m. 

m. 

d. 

d. 
d. 

str. 
m. 

str. 
str. 

str. 

str. 

d. 

d. 
m. 

5 
6 
4 
4 
4 
4 

5 
4 

4 
3 

2 
4 

4 
4 
2 

3 

4 

2148.7 
2219.2 
2290.2 
2359.4 
2430.1 
2500.0 

2164.0 
2235.4 

2321.0 
2390.0 

2464.3 
2533.2 

2552.8 
2623.3 
2695.0 

2559.5 
2630.5 

'70'5' 
71.0 
69.2 
70.7 
69.9 

'i'ia' 

'69.0 

70.5 
71.7 

71.0 

fluorescence  series  F.  There  is  some  indication  that  several  other 
absorption  series  may  be  looked  upon  as  associated  with  fluorescence 
series  in  the  same  way.  Thus  the  series  a  may  perhaps  be  associated 
with  a  very  weak  fluorescence  series  falling  between  D  and  E.  Two 
bands  of  such  a  series  were  occasionally  observed  at  1,968.0,  and 
2,053.4  (interval  85.4).  The  interval  between  the  line  at  2,053.4  and 
the  first  line  of  series  a  is  70.6,  which  is  almost  exactly  the  average 
interval  for  the  absorption  series.  Again,  in  the  case  of  series  h  we 
might  expect  an  absorption  band  to  fall  at  2,078.7,  while  series  H  might 
have  a  fluorescence  band  at  nearly  the  same  point,  viz,  2,079.3.  Neither 
band  was  observed;  but  it  must  be  remembered  that  the  detection  of 
reversible  bands  is  only  possible  when  the  conditions  of  excitation  are 
suitable.  Any  trace  of  fluorescence  tends  to  mask  an  absorption  band, 
and  vice  versa.  The  scarcity  of  bands,  either  of  fluorescence  or  absorp- 
tion, in  the  ''reversal  region"  lying  between  2,060  and  2,120  is  perhaps 
due  to  this  cause.  There  are  other  cases  which  suggest  the  same  rela- 
tionship between  fluorescence  and  absorption  series,  although  less 
definitely. 

While  there  are  thus  strong  reasons  for  believing  that  certain  fluores- 
cence series  are  to  be  looked  upon  as  associated,  in  the  manner  indi- 
cated above,  with  absorption  series,  yet  there  are  several  series  in  the 
fluorescence  spectrum  for  which  no  related  absorption  series  have  been 
observed;  and,  on  the  other  hand,  there  are  several  absorption  series 
which  do  not  appear  to  be  related  with  the  observed  fluorescence.    In 


THE    NITRATES   AND    PHOSPHATES.  127 

this  respect  the  systematic  relation  of  fluorescence  and  absorption  is 
not  so  completely  brought  out  as  in  the  spectra  of  the  chlorides. 

The  observed  intervals  between  bands  are  not  so  nearly  constant  in 
the  case  of  the  absorption  series  as  in  the  fluorescence  series.  It  seems 
to  us  probable  that  this  is  due  to  the  greater  uncertainty  in  the  wave- 
length determinations;  for  on  account  of  the  lack  of  sharpness  of  the 
absorption  bands  and  their  greater  width,  as  compared  with  fluorescence 
bands,  the  accuracy  that  is  attainable  in  determining  their  location  is 
considerably  less  than  in  the  fluorescence  spectrum. 

It  will  be  noted  also  that  the  interval  between  bands  is  different  for 
different  series.  For  series  e  the  average  interval  is  73.1 ;  for  series  d'  it 
is  71.7;  for  series  /i,  70.3;  while  for  the  two  pairs  of  lines  in  the  ultra- 
violet, which  have  been  designated  as  series  fi  and  7,  the  interval  is  in 
one  case  69.0  and  in  the  other  68.9.  This  change  in  interval  as  we  pass 
from  one  series  to  another,  which  is  too  great  to  be  accounted  for  by 
experimental  errors,  appears  of  especial  significance  when  it  is  remem- 
bered that  in  the  fluorescence  spectrum  the  interval  is  the  same  for  all 
the  series. 

One  of  the  most  puzzling  points  brought  out  by  the  detailed  study  of 
the  observed  spectra  is  the  fact  that  a  considerable  number  of  the 
absorption  bands  are  spaced  with  the  interval  corresponding  to  the 
fluorescence  series,  and  in  some  cases  appear  to  form  a  continuation 
of  these  series.  In  such  cases  the  reciprocal  wave-lengths  for  these 
bands  are  included  in  table  40,  but  are  preceded  by  the  letter  A.  Thus, 
there  are  four  absorption  bands,  in  addition  to  the  reversible  band, 
which  apparently  belong  to  series  F.  If  it  is  assumed  that  they  do 
form  a  part  of  this  series,  the  average  interval  for  the  whole  series  comes 
out  exactly  the  same  as  for  the  fluorescence  bands  alone.  Series  J 
appears  to  include  two  absorption  bands,  and  series  B,  E,  and  G  each 
show  one  band.  On  the  whole,  however,  we  are  inclined  to  look  upon 
these  cases  as  the  result  of  accidental  coincidences  and  to  beheve  that 
the  fluorescence  series  do  not  extend  into  the  absorption  region  beyond 
the  reversible  band. 

The  interval  of  about  70,  which  appears  to  be  characteristic  of  the 
absorption  spectrum,  is  also  found  in  the  fluorescence  spectrum.  Thus 
the  bands  of  series  C  are  displaced  from  those  of  series  E  by  intervals 
ranging  from  69.0  to  70.2.  A  similar  relation  appears  to  exist  between 
series  J  and  series  H,  the  average  displacement  being  70.1.  Between 
series  B  and  A  the  average  shift  is  70.6,  between  series  F  and  H,  68.1, 
between  series  D  and  B,  69.1.  With  the  exception  of  series  I  the  series 
thus  seem  to  be  grouped  in  pairs,  the  interval  between  pairs  being  in 
the  neighborhood  of  70.  It  seems  not  unHkely  that  a  companion  series 
exists  for  I  also,  since  faint  bands  were  occasionally  observed  at  1,826.0 
and  1,911.7  (interval  85.7)  which  are  displaced  by  the  intervals  71.3 
and  71.4  from  the  corresponding  bands  of  series  I. 


128 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


The  Trihydrate:  U02(N03)2+3H20. 

The  trihydrate  crystallizes  in  the  triclinic  system  with  the  axial 
ratios  a  :h  :  c  =  1.2542  :  1  :  0.70053.^  The  crystals  were  grown  by 
evaporating  the  nitric-acid  solution  in  a  desiccator  over  caustic  potash 
and  sulphuric  acid  or  over  calcium  chloride.  To  obtain  large  crystal 
plates  the  bottom  of  a  dish  6  cm.  in  diameter  was  covered  with  the 
solution  to  a  depth  of  about  2  mm.  and  the  solution  was  ^' seeded^* 
near  the  center.  A  cover  was  then  placed  over  the  solution  with  a 
small  opening  at  the  center,  so  that  evaporation  took  place  directly 
over  the  cr^^stal.  The  trihydrate  was  also  obtained  in  the  form  of  a 
fine  powder  by  efflorescence  of  the  hexahydrate  crystals  in  dry  air. 
Although  most  of  the  observations  recorded  below  were  made  with 
single  crystals,  a  few  measurements  w^ere  made,  with  concordant  results, 
on  the  powder.  In  the  fluorescence  spectrum  visual  observations  only 
were  made.  In  the  absorption  spectrum  the  measurements  were  in 
most  cases  photographic. 


•  IW> 

1   .         1 

1          .             1 

J           A     '                B          C            D           E    F 
.III 

0  •         H      1               J         A 

III! 

L         'A         B       C          0     B               F 
1                                1        .                 i 

G 

'   H       1         J          K        L 
1     1             111 

M                'A           BCD          1           F         G    >K 
ANHYDROUS 

1     J             K      L  M 

I9'00 

Fig.  78. — One  group  of  bands  from  the  fluorescence  spectrum  of  each  of  the  salts  studied.  The 
spectrum  of  the  hexahydrate  contains  7  such  groups;  that  of  the  trihydrate,  6;  the  dihy- 
drate,  5;  and  the  anhydrous  salt,  3. 

The  fluorescence  spectrum  of  the  trihydrate  was  found  to  consist  of 
63  bands,  of  which  55  fell  into  12  constant-interval  series  of  from  3  to 
6  bands  each.  The  intervals  for  the  different  series  ranged  from  86.5 
to  87.5,  the  average  being  86.8.  The  reciprocal  wave-lengths  are  given 
in  table  42.  The  numbers  in  parentheses  refer  to  absorption  bands 
which  seem  to  fall  into  the  fluorescence  series.    The  relative  intensities 


*Wyrouboflf.  Sur  quelques  composes  de  ruranium,  Bull.  Soc.  Francaise  Mineral,  32,  349-350.    1909. 


THE   NITRATES   AND   PHOSPHATES.  129 

of  the  bands  are  shown  roughly  in  figure  78,  where  a  typical  group, 
i.  e.,  one  band  from  each  series,  has  been  plotted  for  each  of  the  salts 
studied. 

Table  42.— Series  in  the  fluorescence  spectrum  ofuranyl  nitrate  trihydrcUe,  U02{NOz)i-\-3HiO. 

A.  1677.0,  1765.0,  1851.5,  1938.8,  2025.0,  (2112.7,  2200.2). 

B.  1686.1,  1772.0,  1858.7,  1945.7,  2033.2,  (2120.7). 

C.  1778.7,  1865.1,  1952.9,  2041.1,  (2041.1). 

D.  1699.8,  1785.9,  1873.0,  1959.1,  2046.8,  (2134.0,  2220.6,  2307.9). 

E.  1704.2,  1791.8,  1877.4,  1965.3,  2051.0. 

F.  1629.2,  1715.2,  1802.1,  1889.0,  1976.4,  2064.3? 

G.  1637.2,  1722.8,  1808.7,  1895.3,  1982.3,  2070.7. 

H.  1643.9,  1729.2,  1816.1,  1903.0,  1989.9,  2076.3,  (2076.5,  2251.2). 

I.  1821.3,  1908.9,  1995.9,  (2083.8). 

J.  1741.8,  1828.2,  1915.9,  2002.1,  (2089.7). 

K.  1748.6,  1835.3,  1923.3,  2009.8. 

L.  1667.2,  1755.0,  1842.4,  1930.1.  2017.4,  (2103.5,  2189.2,  2277.9). 

The  second  curve  of  figure  77,  which  shows  the  frequency  of  occur- 
rence of  the  different  possible  intervals  between  the  bands  of  the  fluores- 
cence spectrum,  indicates  a  remarkably  regular  grouping  of  the  bands. 
Besides  the  principal  interval  87  which  is  characteristic  of  the  series  in 
this  spectrum,  a  number  of  other  intervals  are  almost  equally  promi- 
nent, e.  g.,  7,  14,  30,  36,  43.5,  50,  80,  94.  In  the  case  of  each  of  these 
intervals  the  frequency  of  occurrence  is  far  above  the  average.  These 
intervals,  of  course,  correspond  to  the  spacing  of  the  bands  in  the 
groups.  Thus  the  interval  43.5,  which  is  just  half  the  principal  interval 
87.0,  occurs  twice  in  each  group,  the  bands  of  series  K  lying  half-way 
between  the  bands  of  series  F  and  the  bands  of  series  L  half-way 
between  those  of  series  G.  In  each  case  the  two  series  might  be  com- 
bined to  form  a  single  series  with  half  the  interval.  Since,  however, 
the  bands  of  the  combined  series  would  be  alternately  strong  and  weak, 
it  does  not  appear  that  such  a  combination  is  justified. 

In  the  absorption  spectrum  of  the  trihydrate,  48  bands  were  observed, 
several  of  which,  however,  were  so  faint  and  indistinct  as  to  make  their 
existence  doubtful.  As  in  the  case  of  the  hexahydrate,  an  interval 
between  bands  of  a  little  more  than  70  is  of  frequent  occurrence,  and 
37  of  the  bands  (including  all  that  are  strong  and  well  defined)  can  be 
arranged  in  9  constant-interval  series.  The  interval  does  not  appear 
to  be  the  same  for  all  of  these  series,  however.  In  one  case  the  interval 
is  as  high  as  73.8,  while  in  another  case  its  value  is  71.0.  For  most  of 
the  series  the  interval  lies  near  72.0. 

In  many  instances  the  absorption  series  start  with  reversed  fluores- 
cence bands.  Reversals  are  especially  sharp  and  definite  in  the  case  of 
the  final  bands  of  series  C,  G,  H,  and  I  (1/X  =  2,041.1,  2,070.7,  2,076.3, 
2,104.9).  In  other  cases,  the  absorption  series  begins  at  a  point  where 
a  fluorescence  band  might  be  expected,  but  where  none  was  actually 
observed.  Thus,  we  should  expect  the  final  bands  of  series  I,  J,  and  K 
to  lie  at  2,082.7,  2,009.0, and2,096.6  respectively.  These  bandswerenot 
observed,  probably  because  of  the  fact  that  the  three  series  in  question 


130  FLUORESCENCE   OF  THE   URANYL   SALTS. 

are  made  up  of  very  faint  lines.  But  the  first  bands  of  the  absorption 
series  i,  j,  and  k  fall  at  2,083.8,  2,089.7,  and  2,095.6,  and  it  would  seem, 
therefore,  that  they  might  properly  be  looked  upon  as  resulting  from 
the  reversal  of  the  final  bands  of  the  corresponding  fluorescence  series, 
even  though  these  bands  escaped  observation. 

The  reciprocal  wave-lengths  for  the  principal  absorption  series  are 
given  in  table  43.    Each  series  is  lettered  in  such  a  way  as  to  indicate 

Table  43. — Series  in  the  absorption  spectrum  of  uranyl  nitrate  trihydrate  [U02{NOz)2+3H20]. 
b      B=  2033.2  h  =(2033.2)         2107.0        2180.8. 


c 

C  =  2041.1 

c=  2041.1 

2112.7 

2186.7. 

c' 

ry=? 

c'=  2043.3 

2116.0 

2189.7 

2261.0. 

r 

F'=  2058.5 

/'=  2057.6 

2129.0 

2200.2 

2271.7. 

0 

G  =  2070.7 

ff=  2071.7 

2142.7 

2213.2 

2285.7 

2357.9. 

h 

H  =  2076.3 

h  =  2076.5 

2148.6 

2220.6 

2368.0. 

% 

I  =(2082.7) 

i  =  2083.8 

2154.5 

2226.9 

2297.8 

2368.0. 

j 

J  =(2090.0) 

j  =  2089.7 

2162.0 

2235.4 

2307.9. 

k 

K  =(2096.6) 

it  =  2095.6 

2166.7. 

V 

L'=? 

V=  2103.0 

2173.4 

2245.7 

2317.5 

the  fluorescence  series  with  which  it  appears  to  be  related,  e.  g.,  the 
first  band  of  series  c  is  the  reversal  of  the  last  band  of  series  C.  In 
each  case  also  the  reciprocal  wave-length  is  given  for  the  last  band  of 
the  fluorescence  series.  The  numbers  in  parentheses  indicate  bands  that 
were  not  observed,  but  would  be  expected  to  occur  with  the  indicated 
value  of  1/X. 

It  is  to  be  observed  that  no  absorption  series  were  found  which  corre- 
sponded to  the  fluorescence  series  A,  D,  E,  and  L.  On  the  other  hand, 
no  fluorescence  series  were  observed  to  correspond  with  the  absorption 
series  c'  and  V, 

The  Dihydrate:  U02(N03)2+2H20. 

Although  the  dihydrate  has  been  made  by  several  observers,  the 
crystalline  form  does  not  appear  to  have  been  studied.  The  crystals 
used  in  this  investigation  were  in  most  cases  made  by  heating  a  tube 
containing  the  crystallized  trihydrate  to  a  temperature  somewhat 
above  100°  C.  and  passing  through  it  a  current  of  air  which  had  been 
run  through  a  mixture  of  sulphuric  acid  and  nitric  acid  and  over 
phosphorus  pentoxide.  The  melted  trihydrate  slowly  evaporated  and 
recrystallized  as  dihydrate  without  losing  nitric  acid.  The  tube  was 
then  sealed  up  to  prevent  the  entrance  of  moisture.  The  dihydrate 
was  also  prepared  synthetically  by  treating  dry  H2UO4  with  the 
^'monohydrate"  nitric  acid,  the  two  being  sealed  in  a  glass  tube  and 
allowed  to  react.  The  crystals  obtained  were  in  each  case  small,  so 
that  the  observations  were  made  on  a  mass  of  crystals  having  no 
systematic  arrangement  of  the  axes. 

Seventy-four  bands  were  observed  in  the  fluorescence  spectrum,  61 
of  which  fell  into  12  constant-interval  series  of  from  4  to  6  bands  each. 
The  interval  ranged  from  87.6  in  series  F  to  88.3  in  series  A,  but  in 
most  cases  lay  near  the  average  of  all,  viz,  88.1.-^    The  values  of  lA 

^  For  series  C,  which  contained  two  bands  only,  the  interval  was  87.2. 


THE    NITRATES   AND    PHOSPHATES.  131 

are  given  in  table  44,  and  a  typical  group,  consisting  of  one  band  from 
each  series,  is  shown  in  figure  78.  Many  of  the  bands  that  do  not  fall 
into  these  12  series  nevertheless  seem  to  belong  to  similar  series  of 
which  only  2  or  3  bands  could  be  detected.  Two  of  these  suspected 
series  have  been  included  in  figure  78,  where  they  are  indicated  by 
dotted  lines. 

Table  44. — Series  in  tJw  fluorescence  spectrum  ofuranyl  nitrate  dihydrate  [U02{NOt)t-\-2H20]. 


A. 

1676.7 

1765.9 

1853.0 

1942.7 

2030.7 

B. 

1684.9 

1773.7 

1861.6 

1951.0 

2037.9 

C. 

1780.6 

1867.8 

D. 

1609.0 

1695.5 

1783.5 

1871.8 

1959.7 

2047.4 

E. 

1618.9 

1705.9 

1794.4 

1880.3 

1967.5 

F. 

1625.3 

1714.3 

1801.5 

1889.5 

1977.1 

2063.1 

G. 

1632.7 

1721.2 

1808.5 

1896.8 

1985.2 

2072.5 

(2072.7) 

H. 

1637.7 

1725.3 

1814.6 

1900.8 

1989.7 

2077.3 

(2078.2) 

I. 

1641.5 

1729.8 



1905.1 

1993.8 

J. 

1645.3 

1734.6 

1821.2 

1909.0 

1998.4 

K. 

1830.5 

1918.3. 

L.  1658.4         1745.5         1834.9         1923.8        2009.3       (2095.9) 
M.  1751.0         1838.2         1926.8        2015.5       (2102.7        2191.3        2278.0) 

The  absorption  bands  were  located  by  observing  the  spectrum  of 
light  from  a  continuous  source  after  diffuse  reflection  from  a  mass  of 
small  crystals.  Although  the  bands  observed  in  this  way  are  sur- 
prisingly sharp,  the  method  is  not  so  satisfactory  as  that  in  which  the 
light  is  analyzed  after  direct  transmission  through  a  single  crystal. 
It  is  doubtful  whether  the  reflection  method  gives  as  great  accuracy 
in  the  location  of  the  bands,  and  many  of  the  weaker  bands,  which 
would  have  been  easily  detected  if  large  crystals  had  been  available, 
were  probably  not  observed  at  all.  For  this  reason,  perhaps,  the 
absorption  spectrum  of  the  dihydrate  shows  only  four  well-defined 
series.  The  reciprocal  wave-lengths  for  these  series  are  given  in  table 
45.  The  interval  between  bands  is  70.0  for  series  m,  70.4  for  series  jy 
and  71.3  for  series  g  and  h.  In  each  case  the  first  band  in  the  absorp- 
tion series  occupies  nearly  the  same  position  as  the  last  band  in  one 
of  the  fluorescence  series. 

Table  45. — Series  in  the  absorption  spectrum  ofuranyl  nitrate  dihydrate  [U02{N03)t-\-2H20]. 

G=  2072.4  g=  2072.7  2144.7  2215.3. 

H=  2077.3  h=  2078.2  2149.4  2218.9         2290.4         2362.9 

J=  (2085.7)  y=  (2086.1)  2156.6  2227.2         2297.3. 

M=(2103.6)  m=  2102.7  2172.7  2242.7. 

The  Anhydrous  Nitrate. 

Specimens  of  uranyl  nitrate  that  were  in  all  likelihood  anhydr  jus, 
and  which  certainly  contained  less  water  than  the  dihydrate,  were 
prepared  by  allowing  nitric  anhydride,  N2O2,  to  react  with  uranic  oxide. 
The  nitric  anhydride  was  distilled  from  a  mixture  of  nitric  acid  and 
phosphorus  pentoxide,  while  the  uranic  oxide  was  prepared  by  heating 
uranic  acid,  H2UO4.  In  preparing  the  oxide,  the  heating  was  not  con- 
tinued so  long  as  to  completely  drive  off  the  water  from  the  uranic 


132  FLUORESCENCE   OF  THE   URANYL   SALTS. 

acid,  since  when  this  was  done  no  reaction  occurred  between  the  oxide 
and  the  nitric  anhydride. 

At  temperatures  above  30°  C.  the  N2O2  reacts  with  the  mixture  of 
UO3  and  H2UO4  to  form  uranyl  nitrate,  presumably  anhydrous,  and  a 
considerable  amount  of  HNO3.  To  free  the  specimen  from  acid,  the 
tube  containing  it  was  placed  in  a  freezing  mixture  until  the  N2O5  was 
frozen,  when  the  HNO3,  which  still  remained  a  liquid,  was  poured  off. 
This  process  was  repeated  several  times.  While  the  amount  of  water 
remaining  after  this  treatment  must  have  been  extremely  small,  we 
cannot  feel  certain  that  all  traces  were  removed,  and  it  is  possible, 
therefore,  that  the  nitrate  formed  may  have  consisted  in  part  of  the 
monohydrate.  No  fluorescence  bands  belonging  to  the  other  hydrates 
could  be  observed.  The  method  of  preparation  was  varied  by  changing 
the  temperature  at  which  the  reaction  was  allowed  to  occur,  and  by 
heating  the  salt,  after  it  had  been  formed,  to  different  temperatures 
and  for  different  periods. 

The  fluorescence  spectra  of  the  different  preparations  differed  widely. 
In  one  case  the  spectrum  was  found  to  consist  of  3  narrow  bands  only, 
but  in  all  other  cases  bands  were  observed  which  remained  broad 
(about  100  A.  u.)  even  at  the  temperature  of  liquid  air.  These  bands 
were  spaced  with  a  constant-frequency  interval  of  approximately  88 
to  89.  It  seems  probable  that  these  broad  bands  were  due  to  the 
solution  of  the  anhydrous  salt  in  nitric  acid.  To  test  this  point  a 
specimen  was  prepared  under  conditions  which  made  certain  the 
presence  of  a  considerable  excess  of  nitric  acid.  The  fluorescence 
spectrum  contained  two  series  of  broad  bands,  the  central  band  of  the 
stronger  series  lying  at  1/X  =  1,939.0  and  that  of  a  weaker  series  at 
1/X  =  1,920.0.  The  specimen  was  then  gently  heated  and  the  nitric 
acid  driven  off  was  condensed  in  a  connecting- tube.  After  this  process 
had  continued  for  a  short  time,  several  series  of  narrow  bands  or  lines 
appeared  in  the  fluorescence  spectrum  (at  —186°  C).  As  this  pro- 
cedure was  repeated,  the  line  spectrum  became  more  prominent  and  the 
broad  bands  fainter.  In  one  instance  the  specimen  was  heated  nearly 
to  decomposition — in  fact,  part  of  the  salt  was  undoubtedly  decom- 
posed— and  in  this  case  the  very  faint  fluorescence  spectrum  consisted 
of  three  narrow  bands  only.  The  same  three  bands  were  observed  in 
the  case  of  most  of  the  specimens  that  were  prepared  in  the  attempt  to 
remove  the  water  of  crystallization,  although  in  other  cases  they  were 
accompanied  by  other  lines  or  broad  bands.  It  seems  probable  that 
these  three  bands  constitute  the  brightest  part  of  the  fluorescence 
spectrum  of  the  anhydrous  salt,  and  that  the  additional  lines  and  bands 
that  were  observed  in  some  specimens  are  due  to  traces  of  the  mono- 
hydrate  or  to  a  solution  of  the  nitrate  in  HNO3.  The  three  bands 
formed  a  series  with  the  interval  88.5,  the  central  band  lying  at 
1/X  =  1,902.0. 


THE   NITRATES   AND   PHOSPHATES.  133 

Summary  of  Section  I. 

(1)  In  the  case  of  each  of  the  nitrates,  the  fluorescence  spectrum  is 
made  up  of  series  in  which  the  intervals  between  bands  are  constant  and 
the  same  for  all  of  the  series.  The  interval  increases  slightly,  but 
unmistakably,  as  the  amount  of  water  of  crystallization  decreases.  For 
the  hexahydrate  the  interval  is  86.0,  for  the  trihydrate  86.8,  for  the 
dihydrate  88.1,  and  for  the  anhydrous  salt  88.5. 

(2)  Numerous  constant-interval  series  occur  in  the  absorption  spec- 
trum, the  interval  being  approximately  71.  But  the  interval  does  not 
appear  to  be  the  same  for  different  series,  even  when  these  occur  in  the 
spectrum  of  the  same  salt.  No  systematic  variation  with  the  amount 
of  water  of  crystallization  could  be  detected. 

(3)  Nearly  all  of  the  series  in  the  absorption  spectrum  have  their 
origin  in  the  '' reversing  region,"  the  first  member  of  the  absorption 
series  being  in  coincidence  with  the  last  member  of  a  fluorescence  series 
and  constituting  a  '^reversible''  band. 

(4)  There  is  some  slight  resemblance  between  the  different  hydrates 
as  regards  the  grouping  of  the  bands  (see  fig.  77).  In  each  case,  for 
example,  a  certain  short  interval  appears  with  a  frequency  consider- 
ably above  the  average.  In  the  case  of  the  hexahydrate  and  the 
dihydrate  this  interval  is  about  8;  in  the  case  of  the  trihydrate  is  almost 
exactly  7.  The  interval  14,  in  the  case  of  the  trihydrate,  and  16,  in  the 
case  of  the  other  two  salts,  is  also  of  unusually  frequent  occurrence. 

(5)  It  is  clear  from  inspection  of  figure  78,  in  which  a  characteristic 
group  of  bands  is  shown  for  each  of  the  hydrates  studied,  that  the 
different  spectra  are  not  in  the  least  similar  in  their  general  appear- 
ance. It  might  at  first  appear  that  the  three  hydrates  have  one  series 
in  common,  viz,  that  designated  as  series  F.  But  while  the  central 
band  of  this  series  does  occupy  practically  the  same  position  in  each  of 
the  three  spectra,  the  fact  that  the  interval  between  bands  is  different 
for  the  different  salts  causes  the  bands  to  fall  more  and  more  out  of 
step  as  we  proceed  in  either  direction  from  the  center  of  the  spectrum. 

On  the  whole,  the  spectra  of  the  different  hydrates  differ  from  one 
another  fully  as  much  as  do  the  spectra  of  two  different  uranyl  salts. 
This  result  is  surprising,  since  it  is  customary  to  think  of  water  of 
crystallization  as  rather  loosely  attached  and  therefore  incapable  of 
exerting  a  great  influence  upon  properties  which  depend  upon  the 
internal  structure  of  the  molecule.  Indeed,  were  the  amount  of  water 
of  crystallization  the  onlv  difference  between  the  forms  of  uranyl 
nitrate  under  consideration,  we  should  look  upon  the  attachment  as 
more  intimate  than  has  generally  been  supposed. 

There  is,  however,  another  distinction,  that  of  crystalline  structure, 
and,  as  will  appear  from  the  subsequent  sections  of  this  chapter,  the 
crystal  form  has  a  profound  influence  upon  the  character  of  the  fluores- 
cence and  absorption  spectra  of  the  uranyl  salts. 


134  FLUORESCENCE    OF   THE   URANYL   SALTS. 

II.  THE  DOUBLE  NITRATES:  INFLUENCE  OF  CRYSTAL  FORM.» 

There  is  good  reason  to  think  that  crystal  form  has  an  important 
bearing  upon  the  structure  and  arrangement  of  fluorescence  spectra. 
The  polarized  spectra  of  the  four  double  uranyl  chlorides,  described 
in  Chapter  VI,  are  almost  identical  in  arrangement  and  in  the  absolute 
position,  relative  intensity,  and  resolution  of  their  bands.  These  sub- 
stances all  crystaUize  in  the  triclinic  system.  Further  evidence  bearing 
upon  this  subject  will  be  found  in  section  iii  of  this  chapter. 

Our  object  in  the  present  section  is  to  describe  the  fluorescence  and 
absorption  of  four  double  uranyl  nitrates  and  to  throw  further  light  on 
the  r61e  played  by  crystal  structure. 

The  two  pairs  of  double  nitrates  studied  are  mono-ammonium  uranyl 
nitrate,  NH4UO2  (NO3)  3  ;di-ammonium  uranyl  nitrate,  (NH4)2TT02(N03)4 
2H2O;  the  mono-potassium  uranyl  nitrate,  KUO2  (N03)3;  and  the 
di-potassium  uranyl  nitrate,  K2U02(N03)4. 

The  crystallographic  features  of  these  four  compounds  may  be 
briefly  specified  as  follows: 

(1)  The  mono-ammonium  salt,  which  crystallizes  from  a  solution  of 
the  two  component  salts  in  concentrated  nitric  acid,  was  described  by 
Meyer  and  WendeP  and  crystallographically  by  Steinmetz.^  The 
crystals  are  of  the  trigonal  system,  with  an  axial  ratio  of  a  :  c  =  1  : 
1.0027. 

(2)  The  di-ammonium  salt  crystallizes  from  a  slightly  acid  water  solu- 
tion of  the  two  salts  in  which  the  ammonium  nitrate  is  in  excess  of  that 
required  for  the  mono-ammonium  salt.  This  salt  was  at  first  thought 
to  be  the  a  modification  of  ammonium  uranyl  nitrate  made  by  Rim- 
bach^  and  measured  by  Sachs,^  but  an  examination  of  the  spectrum  of 
the  a  modification  so-called  proved  that  it  was  simply  uranyl  nitrate 
hexahydrate.  The  crystals  analyzed  by  Rimbach  were  probably  the 
mono-ammonium  form,  as  this  sometimes  forms  in  the  same  solution. 
The  crystals  of  the  di-ammonium  salt  belong  to  the  monoclinic  system. 

(3)  The  mono-potassium  salt  crystallizes  from  nitric-acid  solution 
in  the  rhombic  system,  as  described  by  Steinmetz,  with  axial  ratio 
a  :h  :c  =  0.8541  :  1  :  0.6792. 

(4)  The  di-potassium  salt  crystallizes  with  reluctance;  but  when 
seeded  from  an  acid  aqueous  solution,  it  forms  in  beautiful,  fluorescent 
crystals  of  the  monoclinic  system.  The  axial  angle  is  13  =  90°=*=  and  the 
axial  ratio  a  :b  :c  =  0.6394  : 1  : 0.6190.  The  composition  is  different  from 
that  of  the  di-ammonium  salt,  since  it  lacks  the  water  of  crystallization. 

Both  visual  and  photographic  measurements  of  the  spectra  were 
taken,  and,  since  they  agreed  well,  were  averaged  together.     When 

1  Howes,  H.  L.,  and  D.  T.  WUber:  Physical  Review  (2),  ix,  p.  125  (1917). 

«  Meyei  and  Wendel,  Ber.  d.  d.  Ch.  Ges.,  vol.  36,  4055.     1903. 

'  Steinmetz,  Groth's  Chem.  Krys.,  ii,  p.  150. 

*  Rimbach,  Ber.  d.  d.  Ch.  Ges.,  vol.  37,  472.     1904. 

^  Sachs,  Zeitschr.  f.  Krys.,  vol.  38,  497.     1904. 


THE   NITRATES  AND   PHOSPHATES. 


135 


possible  the  absorption  spectrum  was  obtained  by  transmitted  light. 
The  crystals  from  an  acid  solution  were  of  a  deeper  green  color  than 
those  from  a  water  solution,  which .  necessitated  grinding  to  about 
0.4  mm.  thickness  to  make  them  sufficiently  transparent.  Since  the 
immersion  in  liquid  air  spoiled  a  crystal,  many  crystals  of  each  form 
had  to  be  prepared. 

Since,  as  is  usual  with  the  uranyl  salts,  we  have  in  these  spectra  series 
of  constant-frequency  intervals,  the  location  of  the  bands  (tables 
46,  47,  48,  49)  is  indicated  in  frequency  units.  As  elsewhere  in 
this  treatise,  fluorescence  series  are  denoted  by  capital  letters  (A,  B, 
C,  etc.)  and  the  related  absorption  series  by  a,  6,  c,  etc.,  or  where  the 
relation  is  not  obvious,  by  Greek  letters. 

The  four  spectra  are  mapped  in  the  usual  manner  in  figure  79. 


.6^ 


FLUORESCENCE 


'.5/x 


I   I  illlllllll  llilllliillillll 


ABSORPTION 


.4yx 


■■ll'lllhHI    I. 


Ii  I  lilli  I  Mill 


iiUliJ 


TT 


n 


3. 


Tl 


rnnr 


I'li'iii'i'iiifi'ii 


iriTTF 


'  il-li  I  iliiiii  ili'I'i  'I'llii 


4. 


LikiJ lull  II I  liillili  I 


jjy 


n 


Illlllllll  mil 


r^Mi 


Yxiepo 


IT 


2000 
i 


2400 


Fig.  79. — 1.  Fluorescence  and  absorption  spectra  of  mono-ammonium  uranyl  nitrate,  NH4UO 
(N03)3.  2.  Diammonium  uranyl  nitrate,  (NH4)2U02(N03)4.2H20.  3.  Mono-potassium 
lu-anyl  nitrate,  KU02(N03)3.     4.  Di-potassium  uranyl  nitrate,  K2U02(N03)4. 

In  the  spectra  of  these  double  nitrates,  the  relation  of  absorption  to 
fluorescence  is  somewhat  simpler  than  is  the  case  with  the  uranyl 
nitrates  described  in  section  i  of  this  chapter,  but  it  is  less  systematic 
and  complete  than  in  the  spectra  of  the  double  chlorides.  Thus,  in 
mono-ammonium  and  mono-potassium  salts  (table  46  and  48),  there  are 
not  sufficient  absorption  series  to  match  all  the  fluorescence  series, 
but  there  are  no  absorption  series  that  do  not  join.  In  the  di-ammonium 
spectrum  (table  47)  there  is  a  related  absorption  series  for  each  fluores- 
cence series  and  three  extra  absorption  series  that  are  not  obviously 
related  to  fluorescence.  (Seeplatel,6.)  In  the  spectrum  of  the  di-potas- 
stum  salt,  fluorescence  series  B,  D,  G,  I,  and  J  have  no  corresponding 
absorption  of  measurable  intensity,  while  there  are  two  absorption 
series,  V  and  g,  apparently  with  a  direct  reversing  linkage  with  the 
fluorescence.    As  to  the  completeness  of  classification  of  bands,  it  can 


136 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


be  said  that  not  a  fluorescence  or  absorption  band  of  any  of  the  salts 
fails  to  fit  into  one  of  the  constant-frequency  series. 

Table  46. — Series  in  the  fluorescence  spectrum  of  mono-ammonium  uranyl  nitrate. 


1/X 

A(l/X) 

1/X 

A(l/X) 

1/X 

A(l/X) 

A 
B 

D 

1797.6 
1885.9 
1972.1 
2058.3 

1629.4 
1718.1 
1805.9 
1893.4 
1984.1 

1555.5 
1645.1 
1734.0 
1821.0 
1909.1 
1996.9 
2086.1 

88.3 
86.2 
86.2 

88.7 
87.8 
87.5 
90.7 

89.6 
88.9 
87.0 
88.1 
87.8 
89.2 

G 
I 

1573.9 
1663.0 
1751.0 
1838.2 
1925.9 
2013.8 
2101.3 

1670.0 
1758.0 
1845.7 
1934.2 
2022.3 
2110.2 

1852.5 
1941.4 

89.1 
88.0 
87.2 
87.7 
87.9 
87.5 

88.0 
87.7 
88.5 
88.1 
87.9 

88.9 

"1 

L 

M 

1859.1 
1948.8 
2035.8 

1602.1 

1692.7 

1780.9 

1869.0 

1953.5  1 

2041.0 

1704.2 
1790.4 
1878.8 
1964.9 
2050.6 

89.7 
87.0 

90.6 

88.2 
88.1 
84.5? 
87.5 

86.2 
88.4 
86.1 
85.7 

Series  in  the  absorption  spectrum  of  mono-ammonium  uranyl  nitrate. 

i/x 

A(l/X) 

1/X 

A(l/X) 

1/X 

A(l/X) 

a 

2132.8 
2207.1 
2280.5 
2356.3 
2430.1 
2502.5 

74.3 
73.4 
75.8 
73.8 
72.4 

d 
0 

2163.1 
2237.3 
2313.2 
2386.9 

2469.1 

2621.9 
2693.9 

74.2 
75.9 
73.7 

76.4X2 
72.0 

i 

2111.0 

2187.7 
2412.5 
2562.1 

76.7 
74.9 
74.8 

In  section  i  it  was  shown  that  in  the  spectrum  of  the  uranyl  nitrate 
the  intervals  of  the  fluorescence  series  are  the  same  for  all  series  within 
the  errors  of  observation;  in  the  case  of  the  absorption  series,  however, 
the  interval  is  not  the  same  for  all  series.  In  the  double  nitrates  we 
find  an  unmistakable  variation  in  the  fluorescence  intervals  as  well  as 
in  the  absorption.  In  the  mono-ammonium  nitrate  the  interval  varies 
from  86.4  for  series  M  to  89.0  for  series  B.  In  the  di-ammonium  nitrate 
the  interval  varies  from  83.7  for  G  to  85.0  for  E.  In  the  mono-potas- 
sium nitrate  spectrum  the  interval  varies  between  86.4  for  G  and  87.9 
for  J.  In  the  di-potassium  nitrate  the  interval  varies  between  86.2 
for  E  and  87.6  for  J. 

The  variation  of  the  interval  in  the  absorption  series  is  of  the  same 
order  of  magnitude;  e.  g.y  an  extreme  variation  of  1.4  in  the  mono- 
ammonium,  3.5  in  the  di-ammonium,  4.3  in  the  mono-potassium,  and 
4.4  in  the  di-potassium  nitrate.  In  this  connection  it  was  thought  to 
be  of  interest  to  compare  the  ratios  of  related  fluorescence  and  absorp- 


THE   NITRATES   AND   PHOSPHATES. 


137 


tion  intervals.  In  table  50  these  ratios  are  given.  The  ratios  are 
nearly  constant  for  the  mono-ammonium  and  mono-potassium  uranyl 
nitrates,  but  differ  in  the  case  of  the  other  two  salts. 

Table  47. — Series  in  the  fluorescence  spectrum  of  di-ammonium  uranyl  nitrate. 


lA 

A(lA) 

lA 

A(lA) 

lA 

AdA) 

a| 

B 
C 

D 

1773.6 

1857.4 
1941.8 
2026.4 

1695.6 
1779.5 
1864.4 
1949.3 

1786.4 
1871.6 
1955.2 
2039.6 

1628.8 
1713.1 
1796.3 
1880.8 
1965.2 
2050.2 

83.8 
84.4 
84.1 

83.9 
84.9 
84.9 

85.2 
83.6 
84.4 

84.3 
83.2 
84.5 
84.4 
85.0 

G 
I 

1637.7 
1722.5 
1806.8 
1891.1 
1976.5 
2061.9 

1564.0 
1650.0 
1733.3 
1816.8 
1900.8 
1985.3 
2068.5 

1572.9 
1657.8 
1741.6 
1824.5 
1908.5 
1993.2 
2076.9 

84.8 
84.3 
84.3 
85.4 
85.4 

86.0 
83.3 
83.5 
84.0 
84.5 
83.2 

84.9 
83.8 
82.9 
84.0 
84.7 
83.7 

1664.5 
1748.7 
1832.2 
1918.2 
2002.5 
2084.6 

1754.1 
1838.0 
1923.1 
2008.0 

1595.4 
1681.0 
1764.4 
1847.9 
1931.2 
2015.9 

84.2 
83.5 
86.0 
86.3 
82.1 

83.9 
85.1 
84.9 

85.6 
83.4 
83.5 
83.3 

84.7 

Series  in  the  absorption  spectrum  of  di-ammonium  uranyl  nitrate. 

lA 

AdA) 

lA 

A(lA) 

1/X 

AdA) 

a 

b 
c 

d- 

2114.8 
2185.4 
2254.7 
2531.0 
2669.5 

2178.1 
2248.7 
2321.3 
2392.6 

2124.5 

2332.5 

2401.3 

^    2472.2 

2344.9 
2414.9 

2484.7 

2552.8 

,    2621.2 

70.6 

69.3 
69.1X4 
69.3X2 

70.6 
72.6 
71.3 

69.3X3 
68.8 
70.9 

70.0 
69.8 
68.1 
68.4 

g 

i 

r 

2131.0 
2201.0 

2268.8 
2338.4 
2408.3 
2477.4 
2545.6 
2683.8 

2140.8 
2210.9 
2279.1 

2077.3 
2148.2 
2218.0 
2291.0 
2358.5 
2429.2 
2497.7 
2567.0 

2154.2 
2224.3 
2365.4 
2436.1 
2504.2 

70.0 
67.8 
69.6 
69.9 
69.1 
68.2 
69.1X2 

70.1 
68.2 

70.9 
69.8 
73.0 
67.5 
70.7 
68.5 
69.3 

70.1 

70.6X2 

70.7 

68.1 

A; 

l\ 
a 
b 

r 

2092.9 
2163.9 
2233.2 
2304.0 
2373.8 
2443.6 
2511.1 
2584.7 
2657.5 

2102.3 
2173.9 
2245.1 
2316.8 

2384.8 
2454.2 
2523.3 
2592.7 

2422.3 
2490.9 
2559.7 
2628.1 

2538.1 
2602.2 

71.0 
69.3 
70.8 
69.8 
69.8 
67.5 
73.6 
72.8 

71.6 
71.2 
71.7 

69.4 
69.1 
69.4 

68.6 
68.8 
68.4 

68.1 

138  FLUORESCENCE    OF   THE    URANYL   SALTS. 

Table  48. — Series  in  the  fluorescence  spectrum  of  mono-potassium  uranyl  nitrate. 


1/X 

A(l/X) 

1/X 

A(l/X) 

1/X 

A(l/X) 

B 
D 
F 

1725.3 
1813.8 
1900.4 
1988.1 

1569.1 
1655.9 
1742.7 
1830.2 
1916.3 
2003.8 
2090.5 

1754.1 
1842.3 
1928.5 
2015.7 

88.5 
86.6 
87.7 

86.8 
86.8 
87.6 
86.1 
87.5 
86.7 

88.2 
86.2 
87.2 

G 
J 

1589.8 
1674.8 
1762.0 
1848.5 
1934.9 
2021.4 
2107.8 

1867.6 
1955.1 
2043.2 

85.0 

87.2 
86.5 
86.4 
86.5 
86.4 

87.5 
88.1 

K 
I 

1615.8 

1700.4? 

1790.2 

1877.5 

1964.5 

2050.3 

2136.3 

1683.2 
1769.4 
1856.9 
1943.7 
2030.5 
2118.2 

84.6 
89.8 
87.3 
87.0 
85.8 
86.0 

86.2 
87.5 
86.8 
86.8 
87.7 

Series  in  the  absorption  spectrum  of  mono-potassium  uranyl  nitrate. 

1/X 

A(l/X  ) 

1/X 

A(l/X) 

1/X 

A(l/X) 

d 

2167.0 
2238.3 
2313.8 
2386.1 

71.3 
75.5 
72.3 

^{ 

2117.7 
2189.6 

71.9 

Jfc- 

2140.3 
2213.2 
2287.9? 

72.9 

74.7 

1900       C 
D 

a 

c 

D 

1 

1.              B 
A 

inv 

M 

1 

il 

h^V7 

2.       ' 

aBc 

( 

) 

E 

i 

I         L 

JK  1 
1  1    1 

D 
A?C 

c 

E 

1 
^         L 

f 

C 

3. 

D 

!^ 

C 
B 

1 

) 

F 
1 

I 

@ 

1 

4. 
B        1  EF 

Hi  jKl 

c 

^    1 

> 
EF 

Hi  jKl 
II  1    III 

Fig.  80. — A  single  group  from  each  of  the  four  spectra. 
1.  Mono-potassium    uranyl    nitrate— trigonal.     2.  Di-potassium    uranyl    nitrate— monoclinic. 
3.  Mono-ammonium  uranyl  nitrate — rhombic.     4.  Di-ammonium  uranyl  nitrate — mono- 
climc.     The  bands  occupy  their  natural  positions  in  the  left-hand  panel,  but  have  their 
strongest  bands  in  vertical  alignment  in  the  right-hand  panel. 


THE    NITRATES   AND    PHOSPHATES. 


139 


That  the  crystal  system  to  which  a  salt  belongs  is  an  important  factor 
in  determining  the  position  of  the  bands  can  be  seen  in  figure  80.  In 
the  left-hand  panel  a  single  group  is  shown  in  its  natural  position;  in 
the  right-hand  panel  the  strongest  bands  of  each  group  are  placed  in 
the  same  vertical  line,  to  show  the  resemblance  in  grouping.  This 
similarity  is  probably  due  to  the  fact  that  all  four  belong  to  the  same 
chemical  family.  If  we  compare  this  grouping  with  that  of  the  uranyl 
nitrate  spectra  in  section  i  we  find  little  resemblance,  hence  the 
grouping  is  probably  characteristic  of  the  double  uranyl-nitrate  family. 
In  the  left-hand  panel  it  will  be  seen  that  the  second  and  fourth  groups 
occupy  almost  identical  positions,  while  the  first  and  third  occupy 
positions  which  differ  from  one  another  and  from  the  second  or  fourth. 
As  has  previously  been  stated,  the  second  and  fourth  groups  belong 

Table  49. — Series  of  the  fluorescence  spectrum  of  di-potassium  uranyl  nitrate. 


1/X 

A(l/X) 

1/X 

A(l/X) 

1/X 

AdA) 

B 
D 

E 

1775.2 
1861.9 
1948.9 
2034.6 

1621.3 
1708.0 
1793.7 
1880.0 
1966.9 
2053.7 

1631.6 
1717.9 
1802.7 
1889.3 
1975 . 8 
2062.2 

86.7 
87.0 
85.7 

87.7 
85.7 
86.3 
86.9 
86.8 

86.3 

84.8 
86.6 
86.5 
86.4 

F 
G 

H 

1723.8? 

1808.6 

1894.1 

1980.3 

2068.8 

1554.0 
1640.4 
1727.6 
1813.2 
1899.0 
1986.2 

/1903.7 
\1906.8 

/1989.7 
\1993.8 

/2075.8 
\2080.7 

84.8 
85.5 
86.2 
88.6 

86.4 
87.2 
85.6 
85.8 
87.2 

86.5 
86.6 

I 

f 
J 

K 
L 

1651.5 
1737.6 
1823.8 
1911.2 
1998.5 
2085.5 

1831.8 
1919.5 
2007.0 

1663.3 
1751.8 
1837.8 
1925.1 
2011.9 

1670.8 
1757.8 
1844.6 
1931.4 
2018.3 

86.1 
86.2 
87.4 
87.3 
87.0 

87.7 
87.5 

88.5 
86.0 
87.3 
86.8 

87.0 
86.8 
86.8 
86.9 

Series  in  the  absorption  spectrum  of  di-potassium  uranyl  nitrate. 

1/X 

A(l/X) 

1/X 

A(l/X) 

1/X 

A(l/X) 

fi 

2196.6 
2269.3 

2210.9 
2285.7 

2369.4 
2444.4 

72.7 
74.8 
75.0 

k 

'    2152.6 
2224.3 

'    2169.2 
2240.1 
2310.9 

^    2382.6 

71.7 

70.9 
70.8 
71.7 

i 

8 

2105.9 
2179.9 

2253.4 
2325.1 
2396.9 

2361.6 
2437.8 
2513.2 

74.9 

71.7 
71.8 

76.2 
75.4 

140 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


to  the  monoclinic  crystal  systems,  the  first  to  the  trigonal  and  the  third 
to  the  rhombic  system.  Since  all  four  spectra  vary  slightly  in  their 
frequency  intervals,  the  relative  positions  would  change  slightly  if  we 
compared  homologous  groups  in  the  other  end  of  the  spectrum,  but 
this  gradual  and  slight  shifting  would  not  change  the  general  condition, 
which  indicates  that  the  absolute  position  of  a  group  is  largely  deter- 
mined by  the  crystal  system.  This  is  not  entirely  new,  as  the  four 
triclinic  crystals  of  the  double  uranyl  chlorides  exhibit  spectra  which 
are  as  nearly  coincident  as  could  be  expected  of  salts  which  vary  in 
molecular  weight. 

Table  50. — Average  intervals. 


Mono-ammonium  uranyl  nitrate. 


Fluorescence  series. 


Absorption  seiies 

Ratio  of  fluorescence  to  absorption . 


A 

86.6 


a 
73.7 


1.18 


D 

88.3 

d 
74.5 

1.19 


G 

87.7 

Q 

74.2 

1.18 


I 
88.1 

% 
75.1 

1.18 


Di-ammonium  uranyl  nitrate. 


Fluorescence  series. 


Absorption  series. 


Ratio  of  fluorescence  to  absorp- 
tion   


A 

84.4 

B 

84.4 

C 

84.8 

D 

84.5 

E 
85.0 

G 

83.7 

I 
83.9 

J 

83.8 

K 

84.8 

a 
69.2 

h 
71.6 

c 

69.8 

d 
68.9 

e 

68.7 

g 

68.8 

i 
69.6 

69.7 

k 
70.9 

1.22 

1.18 

1.21 

1.23 

1.22 

1.22 

1.21 

1.20 

1.20 

L 
84.0 

I 
71.5 

1.18 


Mono-potassium  uranyl  nitrate. 


Fluorescence  series. 


Absorption  series 

Ratio  of  fluorescence  to  absorption , 


D 

86.9 

I 
87.2 

d 
73.2 

71.9 

1.18 

1.16 

K 

86.6 

k 
74.1 

1.17 


Di-potassium  uranyl  nitrate. 


Fluorescence  series . 


Absorption  series 

Ratio  of  fluorescence  to  absorption . 


D 
86.6 

E 

86.2 

F 

87.2 

H 

86.5 

K 
86.9 

d 

72.7 

e 

74.8 

/ 
75.0 

h 
71.7 

k 
71.3 

1.19 

1.16 

1.16 

1.21 

1.22 

L 

86.9 

I 
74.9 

1.16 


THE    NITRATES   AND   PHOSPHATES. 


141 


Again,  in  the  case  of  the  uranyl  nitrate,  the  crystals  of  the  hexa- 
hydrate  are  of  the  rhombic  system,  while  those  of  the  trihydrate  and 
dihydrate  are  of  the  triclinic  system.  In  spite  of  slight  shifts  due  to 
changing  molecular  weight,  the  strong  bands  of  the  two  spectra  pro- 
duced by  the  crystals  of  the  triclinic  system  agree  fairly  well,  while  the 
strong  bands  of  the  spectrum  produced  by  the  rhombic  crystal  reside 
in  entirely  different  positions. 

There  is  one  more  bit  of  evidence  which  adds  weight  to  the  above 
view.  The  chemical  formulae  of  the  two  potassium  salts  are  more 
nearly  alike  than  those  of  the  two  ammonium  salts,  since  the  di- 
ammonium  salt  has  2  molecules  of  water  of  crystallization,  while  the 
other  salts  have  none,  yet  there  is  a  greater  difference  between  the 
first  and  second  spectra  than  there  is  between  the  second  and  fourth 
spectra. 

Summary  of  Section  II. 

(1)  The  spectra  of  the  double  uranyl  nitrates  resemble  those  of  the 
previously  studied  uranyl  salts  in  that  the  bands  can  be  arranged  in 
series  having  constant  frequency  intervals. 

(2)  These  intervals,  while  constant  for  any  given  series,  are  different 
for  different  series. 

(3)  In  the  mono-ammonium  uranyl  nitrate  and  the  mono-potassium 
uranyl  nitrate  the  ratio  of  the  interval  of  a  fluorescence  series  to  the 
interval  of  the  absorption  series  which  joins  that  fluorescence  series  is 
approximately  a  constant. 

(4)  Although  the  grouping  of  the  bands  shows  a  strong  family 
resemblance  in  the  four  spectra,  yet  the  absolute  position  of  a  group 
is  largely  determined  by  the  crystal  system. 

III.  RESOLUTION  ON  COOLING  AND  ITS  DEPENDENCE  ON 
CRYSTALLINE  STRUCTURE. 

The  crystal  system  of  any  uranyl  compound  is  an  important  factor 
in  determining  the  character  of  its  fluorescence  and  absorption  spectra, 
as  we  have  endeavored  to  show  in  the  foregoing  section.  There  is 
equally  good  evidence  that  resolution  is  dependent  on  the  existence  of 
a  crystalline  condition. 

Table  51. — Bands  of  fluorescence  in  canary  glass. ^ 


At  +20"  C. 

At  -185°  C. 

X 

1/XX103. 

X 

1/XX103. 

5280 
5180 

1894 
1931 

5330 
5140 

1876 
1946 

1 R.  C.  Gibbs,  Physical  Review  (1),  vol.  30,  p.  382 


142 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Not  all  iiranyl  fluorescence  spectra  are  well  resolved  on  cooling.  In 
the  case  of  a  piece  of  canary  glass,  for  example,  the  rather  unusually 
broad,  vague  doublet  occurs  at  +20°  (see  table  51) . 

At  the  temperature  of  liquid  air  the  doublet  is  partially  resolved, 
but  no  narrow  components  appear. 

The  soUd  solution  of  uranyl  phosphate  in  microcosmic  salt,  the 
phosphorescence  of  which  has  already  been  described  in  Chapter  IV, 
yields  a  narrowing  of  the  bands  on  cooling  and  a  shift,  but  no  resolution. 
(See  table  52.) 

Table  52. — Bands  of  uranyl  phosphate  in  microcosmic  salt.^ 


At  +20«  C. 

At  -185°  C. 

X 

1/XX103. 

X 

1/XX103. 

5670 
5421 
5183 
4970 

1764 
1845 
1929 
2012 

5680 
5430 
5190 
4980 

1761 
1842 
1927 
2008 

^  The  bands  are  160  a.  u.  in  width. 

The  inference  that  the  failure  to  obtain  resolution  of  the  bands  is 
due  to  the  non-crystalline  structure  of  the  substance  is  confirmed  by 
the  observations  described  below. 

EXPERIMENTS  ON  THE  SPECTRA  OF  SODIUM  URANYL  PHOSPHATES.^ 
Stokes,^  in  an  early  paper  on  the  ultra-violet  spark  spectra  of  the 
metals,  described  a  fluorescent  screen  prepared  by  treating  the  ordi- 
nary uranyl  phosphate  with  a  solution  of  phosphoric  acid  and  sodium 
or  ammonium  phosphate.  While  the  uranyl  phosphate  is  only  feebly 
fluorescent,  the  double  salts  thus  produced  were  very  brilliant. 

To  investigate  the  fluorescence  spectra  of  these  double  phosphates, 
the  following  preparations  were  made : 

(1)  A  mixture  of  uranyl  phosphate  and  sodium  phosphate  in  the  ratio  of 
4  molecular  weights  of  HUO2PO4 .  3JH20  to  1  molecular  weight  of  HU02PO4. 

(2)  A  similar  mixture  in  proportions  2  to  1. 

(3)  A  similar  mixture  in  proportions  1  to  1. 

These  three  specimens,  when  cooled  to  —180°  C.  and  excited  by 
radiation  from  the  carbon  arc,  yielded  precisely  similar  and  well- 
resolved  spectra.    (See  fig.  81,  ^,  ;^,  and  3.) 

In  addition  to  the  above,  four  further  specimens  were  made  by 
mixing  increasing  amounts  of  phosphoric  acid  with  sodium  uranyl 
phosphate,  i.  e.: 

(4)  One  molecule  of  phosphoric  acid  to  2  molecules  of  uranyl  phosphate 
and  1  molecule  of  sodium  phosphate,  giving  the  composition  H3NaU02(P04)2 
This  was  a  powder,  similar  to  preparations  1,  2,  and  3. 

1  Howes  and  Wilber,  Physical  Review  (2),  vii,  p.  394.     1916. 
'  Stokes,  Philos.  Trans.,  152,  p.  599.     1862. 


THE   NITRATES  AND   PHOSPHATES. 


143 


(5)  One  molecule  of  phosphoric  acid  to  1  molecule  of  uranyl  phosphate 
and  2  molecules  of  sodium  phosphate.  When  dried,  this  contained  much 
free  sodium  phosphate. 

(6)  Two  molecules  of  phosphoric  acid  to  1  molecule  of  uranyl  phosphate  and 
1  molecule  of  sodium  phosphate.  This  specimen  did  not  dry,  but  remained 
syrupy  at  room  temperature  and  appeared  to  be  vitreous  at  — 180**. 

(7)  A  solution  of  uranyl  phosphate  in  a  considerable  excess  of  syrupy 
phosphoric  acid.     This  gave  a  glass4ike  mass  even  at  +20°. 

The  fluorescence  spectra  of  these  7  substances  are  plotted  to  the 
usual  frequency  scale  in  figure  81 . 

Table  53  gives  the  location  of  the  narrow  bands,  and  approximately 
of  the  crests  of  the  broad,  unresolved  groups;  also  the  frequencies  and 
frequency  intervals. 

It  will  be  seen  that  the  spectra  of  1,  2,  and  3  consist  of  recurring 
groups  of  narrow  bands  and  that  homologous  members  of  these  groups 

Table  53. — Wave-lengths  and  frequencies  of  the  line  series  of  the  fluorescence  of  the  sodium 

uranyl  phosphates. 


X 

lA 

Al/X 

X 

1/X 

AlA 

Series  A 

5640 
5396 
5171 

1773.1 
1853.1 
1933.8 

80.0 
80.7 

Series  F 

6015 
5739 
5484 
5248 
5034 

1662.4 
1742.6 
1823.4 
1905.3 
1986.3 

80.2 
80.8 
81.9 
81.0 

(very  dim) 

Average 

(dim) 

Average 

80.4 

Series  B 

6153 
5862 
5599 
6359 
5136 

1625.2 
1705.8 
1785.9 
1865.9 
1947.0 

80.6 
80.1 
80.0 
81.1 

81.0 

(dim) 

Averafiie 

Series  G 

5460 
5227 
5014 

1831.6 
1913.0 
1994.6 

81.4 
81.6 

(dim) 

Average 

80.5 

81.5 

Series  C 

6114 
5827 
5568 
5327 

1635.7 
1716.0 
1796.0 
1877.3 

80.3 
80.0 
81.3 

Series  H 

(very  dim) 

5429 
5199 
4989 

1841 . 8 
1923.4 
2004.6 

81.6 
81.2 

(very  dim) 

Average 

81.4 

80.5 

80.0 
79.6 
81.5 

♦Series  B'       

6169 
5877 
5607 
5363 
5136 

1621.0 
1701.5 
1783.5 
1864.6 
1947.0 

80.5 
82.0 
81.1 

82.4 



Series  D 

6075 
5794 
5538 
5299 

1646.0 
1726.0 
1805.6 

1887.1 

(medium) 

Average 

(medium) 

80.4 

Series  E 

(very  strong) 

Average 

6350 
6040 
5760 
5506 
5270 
5057 

1574.9 
1655.7 
1736.2 
1816.2 
1897.4 
1977.6 

80.8 
80.5 
80.0 
81.2 
80.2 

80.5 

*  Series  B'  is  found  in  spectrum  No.  6  only 


144 


FLUORESCENCE    OF  THE   URANYL   SALTS. 


Table  53. — Wave-lengths  and  frequencies  of  the  broad-band  series  of  the  fluorescence  of  the 

sodium  uranyl  phosphates. 


X 

1/X 

Al/X 

X 

1/X 

Al/X 

Spectrum  No.  4 

Average 

6219 
5909 
5641 
5390 
5158 
4948 

1608.0 
1692.6 
1772.7 
1855.3 
1938.7 
2021.0 

83.6 
80.1 
82.6 
83.4 
82.3 

Spectnun  No.  6 .  . . . 
Average 

5932 
5644 

5388 
5147 

1685.8 
1771.8 
1856.0 
1942.9 

86.0 
84.2 
86.9 

85.3 

82.6 

Spectrum  No.  7 .  . . . 
Average 

5958 
5661 
5400 
5157 
4935 

1678.4 
1766.5 
1851.9 
1939.1 
2026.4 

88.1 
85.4 
87.2 
87.3 

Spectrum  No.  6 

Average 

5927 
5647 
5398 
5174 
4956 

1687.2 
1770.9 
1852.5 
1932.7 
2017.8 

83.7 
81.6 
80.2 
85.1 

87.0 

82.7 

Mill 


ill 


±11} 


II   I  I 


ll    II  li 


2. 


nil 


.III 


i± 


Mil  ll 


^JU. 


Ill 


iui 


tl   ■  I 


I..M     I, 


.Zkii 


ZW 


form  the  usual  constant-interval  series.  The  interval,  which  is  the 
same  for  all  within  the  errors  of  observation,  is  the  shortest  yet  observed 
in  the  study  of  the  fluorescence  of  the  uranyl  salts.  Position  as  well  as 
the  arrangement  of  the  bands  is  identical,  and  it  is  highly  probable 
that  we  have  to  do  with  the  same 
crystalline  fluorescent  compounds  in 
these  three  preparations.  f^ 

The  broad  bands  of  specimens  4  and 
5  form  series  with  a  constant  interval 
of  82.5  units.  Evidently  the  increase 
in  the  proportion  of  phosphoric  acid 
tends  to  suppress  the  strongest  line 
series  and  merge  the  dimmer  series 
into  broad  bands.  With  the  increas- 
ing predominance  of  the  broad  bands, 
caused  by  the  increasingly  larger  pro- 
portion of  acid  present,  there  is  a  si- 
multaneous increase  in  interval  from 
82.5  units  to  85.1  units  for  specimen 
No.  6,  and  87.0  units  for  specimen 
No.  7. 

Experiments  similar  to  the  above 
were  made  in  which  ammonium  phos- 
phate was  substituted  for  sodium  phos- 
phate. The  results  were  in  all  respects 
analogous  to  those  above  described. 

That  in  general  the  resolution  of  the  uranyl  spectra  by  cooling  occurs 
only  when  the  fluorescing  substance  is  in  crystalline  form  is  further 
substantiated  by  numerous  experiments  on  frozen  solutions  to  be 
described  in  detail  in  Chapter  X. 


Ma 


^x 


/\  f)i\[\ 


x>  /\  /A  A 


V\r\Ar\ 


jilftfi. 


JfllflSL 


l»}99 


Fig.  81. 


THE   NITRATES   AND   PHOSPHATES.  145 

Summary  of  Section  III. 

(1)  Where  uranyl  compounds  occur  in  solid  solution,  as  in  canary 
glass,  or  in  a  bead  of  microcosmic  salt,  the  banded  fluorescence  spec- 
trum with  constant  frequency  intervals,  as  observed  at  +20°  C,  is 
not  further  resolved  into  groups  of  narrow,  line-like  bands  by  cooling 
to  the  temperature  of  liquid  air. 

(2)  Sodium  uranyl  phosphate  or  ammonium  uranyl  phosphate, 
when  prepared  in  the  form  of  crystalUne  powder,  gives  fluorescence 
spectra  which  are  fully  resolved  at  low  temperatures. 

(3)  In  the  presence  of  an  excess  of  phosphoric  acid,  where  the 
above  compounds,  or  uranyl  phosphate,  form  solid  solutions  of  vitreous 
structure,  resolution  does  not  occur  on  cooling. 

(4)  There  is  reason  to  think  that  the  dependence  of  resolution  by 
cooling  upon  the  existence  of  crystalline  structure  applies  in  general 
to  the  fluorescence  of  the  uranyl  salts. 


VIII.  THE  ACETATES. 

The  uranyl  acetates  afford  a  broader  field  for  investigation  than  the 
chlorides  or  nitrates,  the  spectra  of  which  have  been  considered  in 
previous  chapters. 

In  addition  to  two  forms  of  the  single  acetate  UO2  (€211302)2,  we  have 
the  double  salts  of  all  the  alkali  metals  except  caesium;  the  double  salts 
of  calcium,  barium,  strontium,  magnesium,  zinc,  lead,  silver,  and 
manganese;  the  triple  salt  NaMg  UO2 (0211302)5. 

In  the  fluorescence  spectra  of  the  acetates,  as  in  the  case  of  all 
uranyl  salts  thus  far  studied,  the  broader  bands  observed  at  room 
temperature  are  resolved  into  groups  when  the  substance  is  excited 
at  the  temperature  of  liquid  air,  and  the  constitution  of  these  groups, 
which  repeat  themselves  at  regular  intervals  from  the  red  to  the  region 
in  the  blue,  where  absorption  begins  to  replace  fluorescence,  is  very 
similar  in  the  acetates  to  that  of  the  groups  in  the  spectra  of  the  com- 
pounds already  discussed. 

THE  SINGLE  ACETATE. 

Two  distinct  varieties  of  this  salt  were  available  for  observation — 
the  finely  powdered  anhydrous  form,  U02(C2H30i)2,  and  the  crystalline 
form,U02(C2H302)2.H20. 

The  spectra  of  the  two  are  very  similar  in  appearance;  each  being 
characterized  by  two  strong,  well-defined  series  forming  a  set  of  doub- 
lets. They  are  easily  distinguished,  however,  by  the  widely  different 
location  of  the  doublets.  In  the  spectrum  of  the  anhydrous  variety 
these  occur  near  the  group  centers  of  the  alkaline  double  salts,  whereas 
in  the  crystalline  form  they  fall  nearly  midway  between  these  groups. 

The  strong  series  of  the  crystalline  salt,  which  we  have  denoted  as 
E  and  F,  frequently  appear  in  greatly  reduced  intensity  in  the  spectra 
of  the  double  salts,  due  doubtless  to  the  presence  of  traces  of  the  single 
acetate.  The  strong  doublets  C  and  D  of  the  anhydrous  acetate, 
if  they  ever  appear  in  the  spectra  of  the  double  salts,  would  be  more 
difficult  to  detect,  as  they  would  overlap  bands  in  the  groups  of  the 
latter. 

Wave-lengths  and  frequencies  of  these  two  forms  of  uranyl  acetate 
are  given  in  tables  54  and  55.  Intensities  are  designated  as  very  strong 
(vs),  strong  (s),  medium  (m),  dim  (d),  very  dim  (vd),  and  very  very 
dim  (wd). 

Studies  of  a  Single  Group. 

Since  the  acetates,  like  the  chlorides  and  nitrates  discussed  in  pre- 
vious chapters,  have  spectra  consisting  of  similar  recurring  groups, 
it  is  convenient  and  sufficient,  in  the  study  of  the  structure  of  the 
ensemble  of  the  fluorescence,  to  consider  a  single  group.     For  this 

146 


THE   ACETATES.  147 

Table  54. — Fluorescence  hands  in  spectrum  of  uranyl  acetate  (anhydrous),  —IBS'*. 


Group. 

Series. 

A* 

1/mX10' 

Int. 

Group. 

Series. 

M 

i/mxio» 

Int. 

o, 

C" 

0.6037 

1656.4 

m. 

A 

0.5295 

1888.5 

d. 

D 

.6011 

1663.5 

m. 

B 

.5273 

1896.6 

d. 

E 

.5975 

1673.6 

vd. 

C 

.5229 

1912.5 

d. 

F 

.5950 

1680.6 

vd. 

C' 

.5223 

1914.4 

8. 

6j 

D 

.5202 

1922.4 

S. 

A 

.5822 

1717.5 

d. 

E 

.5183 

1929.4 

vd. 

B 

.5799 

1724.3 

d. 

F 

.5161 

1937.5 

m. 

C 

.5749 

1739.4 

d. 

G 

.5117 

1954.4 

vd. 

4 

C 
D 

.5739 
.5713 

1742.6 
1750.5 

m. 
m. 

H 

.5088 

1965.5 

vd. 

E 

.5687 

1758.5 

vd. 

A 

.5062 

1975.4 

vd. 

F 

.5663 

1765.7 

vd. 

B 

.5041 

1983.6 

vd. 

7 

C' 

.5006 

1997.4 

d. 

A 

.5548 

1802.6 

d. 

D 

.4979 

2008.6 

s. 

B 

.5523 

1810.5 

d. 

E 

.4961 

2015.6 

vd. 

C 

.5481 

1824.6 

d. 

F 

.4940 

2034.3 

d. 

C 

.5469 

1828.5 

s. 

5 

D 
E 
F 
G 

.5445 
.5424 
.5401 
.5352 

1836.4 
1843.6 
1851.5 
1868.5 

8. 

d. 

d. 

vd. 

H 

.5318 

1880.5 

vd. 

Table  55. — Fluorescence  bands  in  spectrum  of  uranyl  acetate  {U0'i{CiHz0i)i-\-2HiO\, 

at  +185°  C. 


Group. 

Series. 

/* 

1/mX103 

Int. 

Group. 

Series. 

M 

1/mX10» 

Int. 

A 

E 

0.6158 

1623.9 

d. 

A 

0.5166 

1935.7 

vd. 

F 

.6133 

1630.5 

m. 

B 

.5149 

1942.3 

d. 

C 

.5130 

1949.2 

d. 

[ 

E 

.5860 

1706.6 

m. 

C' 

.5122 

1952.0 

vd. 

4 

E' 

.5849 

1709 . 8 

m. 

D 

.5107 

1958.0 

vd. 

\ 

F 

.5825 

1716.8 

s. 

7 

El 

.5096 

1962.3 

d. 

E 

.5090 

1964.6 

m. 

B 

.5648 

1770.5 

vd. 

Fl 

.5075 

1970.4 

s. 

C 

.5630 

1776.1 

vd. 

F 

.5067 

1973.5 

8. 

El 

.5583 

1791.2 

vd. 

F' 

.5059 

1976.7 

vd. 

E 

.5575 

1793.6 

m. 

G 

.5027 

1989.1 

vd. 

6 

F 

.5550 
.5529 

1801.9 
1808.8 

s. 
vd. 

H 

.5005 

1998.2 

vd. 

G 

.5504 

1816.9 

vd. 

A 

.4962 

2015.3 

d. 

H 

.5473 

1827.0 

vd. 

B 

.4930 

2028.5 

m. 

I 

.5442 

1837.6 

vd. 

C 
C' 

.4913 
.4904 

2035.5 
2039.2 

m. 
d. 

Ai 

.5416 

1846.4 

vd. 

8 

D 

.4892 

2044.1 

d. 

B 

.5385 

1857.0 

d. 

Fl 

.4863 

2056.3 

m. 

C 

.5367 

1863.3 

d. 

F 

.4857 

2058.7 

m. 

C' 

.5357 

1866.7 

vd. 

F' 

.4848 

2062.7 

8. 

D 

.5342 

1872.1 

vd. 

G 

.4823 

2073.2 

vd. 

6 

El 
E' 
F 
F' 
F' 
G 

.5329 
.5322 
.5305 
.5300 
.5289 
.5258 

1876.5 
1878.9 
1885.0 
1886.7 
1890.7 
1901.9 

d. 
m. 
vd. 

8. 

vd. 
vd. 

H 

.5231 

1911.7 

vd. 

148 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


purpose  group  7,  which  is  in  the  brightest  part  of  the  spectrum  and  is 
free  from  the  complications  due  to  the  overlapping  of  fluorescence  and 
absorption  in  the  reversing  region,  is  most  favorable.  In  figure  82 
the  spectral  region  of  this  group  is  plotted  for  the  anhydrous  and 
crystalline  forms  of  the  single  acetate  to  depict  the  remarkable  dis- 
placements brought  about  by  the  presence  of  water  of  crystallization 
and  the  consequent  modifi- 
cation of  crystal  structure. 
The  effect  is  very  similar, 
both  as  regards  the  direction 
of  the  shift  of  the  groups  and 
the  amount  of  shift,  to  that 
already  described  in  the  case 
of  the  nitrates.  (Compare 
fig.  78  in  Chapter  VII.) 

In  both  instances  it  is  not 
the  transfer  of  the  groups 
toward  the  blue  without 
change  in  their  structure  that 
occurs,  but  something  much 
less  obvious.  In  fact,  it  is  not  possible  to  identify  any  of  the  bands 
in  the  spectra  of  the  hydrated  form  with  those  belonging  to  the  an- 
hydrous salt. 

To  produce  this  change  in  the  spectrum  it  is  only  necessary  to  add 
a  drop  of  water  to  a  small  portion  of  the  anhydrous  powder  and  to 
compare  the  fluorescence  of  the  dry  and  moistened  substance  when 
excited  in  the  usual  way  at  — 185°. 

Frequency  Intervals  of  the  Single  Acetates. 

The  frequencies  and  frequency  intervals  of  the  series  occurring  in 
the  spectra  of  the  two  forms  of  the  single  acetates  are  given  in  tables 
56  and  57,  from  which  it  will  be  seen  that  the  two  forms  of  the  acetate 


Uranyl 

ACCTATC 

Anhijdrous 

A     B 

1       .     ,       1 

c 
1 

1 

D 

F 

1 

G        H                            1 
1          1         i       1            1 

CrystoUii 

Mill 

■>e 

1 

8    C 
1        1                    1 

F 
D                         G 

,1:  1.       . 

1900 


Fig.  82. 


Table  56 

— Uranyl  acetate  (anhydrous). 

Series. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Average 
interval. 

A 

1717.5 
1724.3 
1739.4 
1742.6 
1750.5 
1758.5 
1765.7 

1802.6 
1810.5 
1824.6 
1828.5 
1836.4 
1843.6 
1851.5 
1868.5 
1880.5 

1888.5 
1896.6 
1912.5 
1914.4 
1922.4 
1929.4 
1937.5 
1954.4 
1965.5 

1975.4 
1983.6 
1997.4 
2000.6 
2008.6 
2015.6 
2024.8 

85.97 
86.40 
86.00 
86.00 
86.27 
85.50 
85.91 
85.90 
85.00 

B 

Ci 

C 

1656.4 
1663.5 
1673.6 
1680.6 

D 

E 

F 

G 

H 

General  average .  . 

85.96 

THE   ACETATES, 


149 


appear  to  have  the  same  interval.  The  difference  between  the  weighted 
averages  is  much  less  than  the  uncertainties  in  the  determination  of 
the  intervals  of  the  dim  bands  of  the  weaker  series. 


Table  57.— 

Uranyl  acetate  (crystalline; 

2H,0). 

Series. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

A2 

2015.3 

Ai 

1846.4 

A 

1935.7 
1942.3 
1949.2 
1952.5 
1958.0 
1962.3 
1964.6 
1970.4 
1973.5 
1976.7 

B 

1770.6 
1776.1 

1857.0 
1863.3 
1866.7 
1872.1 
1876.5 
1878.9 
1885.0 
1886.7 
1890.7 

2028.5 
2035.5 
2039.2 
2044.1 

2058.8 
2062.7 

86.0 

86.45 

86.25 

86.0 

85.23 

85.18 

85.65 

85.66 

86.00 

c 

c 

D 

El     

1706.6 
1709.8 

1791.2 
1793.6 

E 

1623.9 

Fi 

F 

1630.5 

1716.8 

1801.9 

F' 

F" 

1808.8 
1816.9 
1827.0 
1837.6 

G 

1901.9 
1911.7 

1989.1 
1998.2 

2073.2 

85.42 
85.60 

H 

I  

General  average 

86.72 

THE  DOUBLE  ACETATES. 

The  fluorescence  spectra  of  these  salts  have  as  a  rule  lower  frequency- 
intervals  than  the  two  forms  of  single  acetate.  The  average  interval 
is  below  85,  as  compared  with  85.7  for  U02(C2H302)22H20  and  85.9 
for  the  anhydrous  single  acetate. 

The  group  structure  is  in  general  less  symmetrical  than  that  of  the 
double  chlorides  or  the  double  nitrates  and  precise  comparisons  are 
therefore  more  difficult. 

Corresponding  groups  in  the  majority  of  cases,  however,  occupy  very 
nearly  the  same  position  in  the  spectrum,  and  the  system  of  designating 
the  various  bands  employed  in  the  discussion  of  the  chlorides  and 
nitrates  has  been  used. 

If  we  neglect  some  of  the  weaker  outlying  bands,  the  group  structure 
of  several  of  the  double  acetates  is  found  to  consist  of  4  nearly  equi- 
distant bands  the  wave-length  of  which  is  almost  if  not  quite  inde- 
pendent of  the  metal  which  enters  into  the  composition  of  the  double 
salt.  The  substances  which  most  nearly  conform  to  this  type  are  the 
double  acetates  containing  lithium,  potassium,  calcium,  and  strontium. 

Manganese  uranyl  acetate  differs  from  these  only  in  the  absence  of 
band  B  in  some  groups.    (See  fig.  83.) 

In  the  spectrum  of  the  barium  double  acetate  the  groups  are  shifted 
bodily  toward  the  red  about  5  frequency  units.  In  the  spectra  of  the 
ammonium  and  rubidium  salts  band  D  is  doubled. 


160 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


The  double  acetates  of  sodium,  magnesium,  zinc,  silver,  and  lead 
(fig.  84,  a)  are  made  up  of  groups  which,  while  they  overlap,  are  by  no 
means  identical,  either  as  to  the  location  or  arrangement  of  their  bands. 

The  spectra  of  these  5  salts  agree,  however,  in  this:  They  contain 
in  each  group  5  bands  which  correspond  so  closely  with  the  bands 
B,  C,  D,  E,  and  F  of  the  double  acetates  depicted  in  figure  83  that  by 
a  bodily  shift  of  the  group  as  a  whole  they  may  be  made  to  conform 
to  the  uniform  arrangement,  so  far  as  those  bands  are  concerned,  quite 
as  well  as  do  the  latter.  This  may  be  seen  from  figure  84  &,  in  which 
the  dotted  vertical  lines  indicate  the  positions  of  the  bands  in  the  uni- 
form type,  while  the  group  in  each  case  has  been  shifted  so  as  to 
register  approximately. 


OeuaLK 

ACKTATCa 

u 

C 

D 

C 

r 

H 
1 

K 

1 

Ca 

Mn 

1 

1 

Sr 

1 

1 

•» 

BO 

n 

50 

Fig.  83. 


DOUSLC        ACeTATM 

N« 

1 

t    F 

i. 

ill  II 

1 1 

1     It             1 

1    1 

1 

.11,1 

1 
1 

1    1    1 

1      , 

1    1 

Zn 

'1 

Zn      ; 

1 

1      1 

1     M 

M    II 

1      1  1 

.1      1 

As 

1         1 

1  1 

A,   :  i 

1    1 

1 
1 

1 

1 
1 

1 

Pb 

1 

1    1 
Pb      1    j 

1 

ll  1 

.1 

Fig.  84o. 


Fig.  846. 


The  distinction  between  the  spectra  under  discussion  and  those 
previously  considered,  which  were  described  as  having  group  spectra 
conforming  to  an  essentially  uniform  type  both  as  to  location  of  bands 
and  group-structure,  is  twofold:  (a)  there  is  a  shift  of  the  groups  as  a 
whole;  (6)  there  are  additional  series,  varying  in  intensity,  some  of 
which  are  among  the  strongest  in  the  spectra  and  which  are  charac- 
teristic of  the  individual  salt. 

It  should  be  reiterated  in  this  connection  that  neither  the  bands 
B,  C,  D,  E,  and  F,  which,  although  sometimes  uniformly  shifted,  are 
common  to  the  spectra  of  the  double  acetates,  nor  the  additional 
bands,  are  found  in  the  spectra  of  the  single  acetates.  The  spectrum 
of  neither  the  anhydrous  acetate  nor  the  crystalline  form  can  be  made 
to  conform  to  the  uniform  type  by  a  general  shift. 


THE   ACETATES. 


151 


A  Possible  Relation  to  the  Metallic  Spark  Spectra. 

It  appears  from  the  foregoing  that  any  metal  capable  of  forming  a 
double  uranjd  acetate  modifies  the  constitution  of  the  fluorescence 
spectrum  both  as  to  the  composition  of  the  groups  and 
their  location.  Certain  metals,  such  as  lithium,  potas- 
sium, calcium,  manganese,  and  strontium,  produce  one 
and  the  same  modification,  irrespective  of  the  metal  which 
is  present.  Other  metals  shift  the  group  sUghtly  (e.  g., 
barium)  or  vary  slightly  the  relative  distances  between 
neighboring  bands  without  otherwise  changing  the  struc- 
ture of  the  group.  The  presence  of  still  other  metals, 
such  as  sodium,  magnesium,  zinc,  silver,  and  lead,  results 
in  a  considerable  general  shift  and  the  introduction  of 
new  series  into  the  spectrum  characteristic  of  the  partic- 
ular metal  in  question  and  existing  only  in  the  doublet 
salt  of  which  it  forms  a  part.  Some  of  these  groups  are 
much  more  complex  than  the  uniform  type  depicted  in 
figure  83.  The  others  are  accompanied  by  strong  bands  or 
minor  groups  of  bands  lying  outside  the  usual  boundaries. 

One  might  imagine,  to  account  for  this  type  of  spec- 
trum, that  in  addition  to  the  metal  in  combination  as  a 
part  of  the  double  salt,  there  are  in  solution  certain 
other  radiators.  If  these  are  uncombined  particles  of 
the  metal  existing  in  a  condition  akin  to  the  gaseous 
state,  one  might  expect  a  type  of  radiation,  under  exci- 
tation, similar  to  that  discovered  by  Wood^  in  sodium- 
vapor;  I.  e.,  series  of  constant  frequency  made  up  of  bands 
instead  of  lines  because  of  damping.  One  member  of  each 
such  series  should  coincide  or  nearly  coincide  with  some 
line  in  the  arc  or  spark  spectrum  of  the  metal. 

Now,  there  are  in  fact  various  coincidences  or  approxi- 
mations thereto  close  enough  to  bring  lines  of  the 
emission  spectrum  well  within  the  brighter  portion  of 
one  of  the  fluorescence  bands  in  question.  In  the  spec- 
trum of  silver  uranyl  acetate,  for  example,  there  is  a 
strong  series  which  does  not  coincide  with  any  series  in 
the  fluorescence  spectra  of  the  other  acetates  thus  far 
observed.  One  member  of  this  series  coincides  with 
the  brightest  visible  line  in  the  spark  spectrum  of  silver 
(Haschek  0.54655  fx;  frequency  number  1,829.6).  Our 
reading  of  the  corresponding  band,  made  before  we  had 
any  suspicion  of  the  possible  relation  here  suggested,  was 
1,829.8.  The  rather  bright  line  (0.51838)  and  the  neigh- 
boring doublet  (0.51729-0.51675)  in  the  spark  spectrum 
of  magnesium  correspond  similarly  to  bands  1,928.9  and 
1,934.4  of  the  fluorescence  spectrum. 


Fio.  85. 


R.  W.  Wood.     Physical  Review  (2),  xi,  p.  76. 


152  FLUORESCENCE    OF   THE   URANYL   SALTS. 

In  the  spark  spectrum  of  lead,  of  the  9  Unes  listed  by  Haschek  which 
lie  in  the  fluorescence  region,  7  are  within  one  frequency  unit  of  our 
readings  of  the  corresponding  bands;  4  of  these  are  in  practically 
perfect  coincidence,  the  departures  from  the  crests  of  the  bands  being 
onljT^  one  or  two  tenths  of  a  unit. 

Of  the  25  spark  lines  of  zinc  within  the  fluorescence  region,  15  are 
certainly  not  related  to  fluorescence  in  the  manner  here  under  con- 
sideration, 4  in  somewhat  doubtful  coincidence,  and  6  are  in  close 
approximation.  Of  these  last,  5  are  consecutive  lines  of  the  spark 
spectrum,  all  of  which  are  in  group  7  of  our  fluorescence  system.  The 
evidence  of  any  significant  relation  based  upon  these  coincidences  is 
obviously  far  from  conclusive.  The  matter  is  mentioned  here  solely 
in  view  of  possible  developments  in  the  further  study  of  the  connection 
between  fluorescence  and  temperature  radiation. 

The  search  for  possible  coincidences  in  the  case  of  sodium  led  to  the 
discovery  of  a  striking  arrangement,  which  seems  to  be  peculiar  to  that 
element.  The  doublets  and  triplets  of  the  spark  spectrum,  while  they 
do  not  form  constant-frequency  series,  are  so  located  that  they  could 
be  excited  to  radiation  of  the  type  described  by  Wood,  with  a  common 
interval  equal  to  the  fluorescence  interval  of  the  acetates;  ^.  6.,  about 
85,  the  result  would  be  a  well-defined  group  spectrum  of  the  type  of  the 
fluorescence  spectrum  of  the  uranyl  salts.  (See  fig.  85.)  There  are, 
however,  only  two  individual  coincidences  with  bands  of  the  sodium  h 
uranyl  acetate.  H 

In  the  figure,  the  actual  arc-lines  of  sodium  are  elongated.  The 
shorter  lines  are  derived  from  them  by  assuming  constant-frequency 
series  having  the  interval  85,  as  described  above. 


Fluorescence  Series  in  the  Spectra  of  the  Double  Acetates. 

In  tables  58  to  70  the  fluorescence  bands  in  the  spectrum  of  the  double 
salts  are  arranged  in  the  order  of  their  wave-length.  In  tables  71  to 
83  the  frequencies  and  average  intervals  of  each  series  in  the  various 
salts  are  given.  It  will  be  seen  by  comparison  with  tables  56  and  57 
that  the  average  interval  for  the  double  acetates  is  less  by  more 
than  one  frequency  unit  than  for  the  single  acetates;  also  that  the  av- 
erage for  the  various  double  salts  differ  from  the  general  average  of  all 
(table  84)  by  an  amount  no  greater  than  the  difference  between  the 
intervals  of  the  various  series  present  in  the  spectrum  of  a  given  salt. 
In  brief,  whatever  real  differences  may  exist  are  too  small  to  be  deter- 
mined from  our  data. 


I 


THE   ACETATES. 

Table  58. — Lithium  uranyl  acetate. 


153 


Group 

Group 

Group 

and 

/^ 

1//XX103 

Int. 

and 

M 

l/AiX103 

Int. 

and 

/* 

1/mX10» 

Int. 

senes. 

series. 

senes. 

fA 

0.6105 

1638.0 

d. 

C 

0.5481 

1824.5 

m. 

fc 

0.5016 

1993.7 

m. 

3^ 

.6033 

1657.4 

vd. 

D 

.5451 

1834.4 

d. 

D 

.4987 

2005.1 

B. 

.5963 

1677.0 

m. 

5 

E 

.5423 

1844.0 

8. 

7 

E 

.4967 

2013.1 

ms. 

H 

.5858 

1707.0 

vd. 

F 

.5399 

1852.0 

m. 

F 

.4948 

2021 . 1 

ms. 

^ 

.5363 

1864.7 

vd. 

H 

.4889 

2045.6 

d. 

'C 

.5740 

1742 . 1 

d. 

H 

.5336 

1874.1 

vd. 

D 

.5711 

1751.0 

d. 

C 

.4808 

2080.0 

ma. 

4 

E 

.5680 

1760.5 

m. 

C 

.6238 

1909.0 

m. 

8  D 

.4784 

2080.6 

8. 

F 

.5653 

1769.0 

d. 

D 

.5209 

1919.8 

s. 

F' 

.6761 

2104.8 

ms. 

H 

.5590 

1789.0 

vd. 

6^ 

E 

.5184 

1928.9 

8. 

F 

.5166 

1935.8 

m. 

G 

.5128 

1950.2 

vd. 

Ih 

.5102 

1960.2 

d. 

Table  59. — Sodium  uranyl  acetate. 


if 

0.6262 

1597.0 

d. 

Bi 

0.5510 

1816.0 

vd. 

B 

0.6027 

1989.2 

vd. 

.6107 

1637.5 

s. 

B 

.5494 

1820.2 

vd. 

C 

.4998 

2001.0 

m. 

C 

.5468 

1828.8 

m. 

C' 

.4988 

2004.9 

d. 

Bi 

.6085 

1643.5 

m. 

C' 

.5452 

1834.1 

m. 

D 

.4972 

2011.3 

V8. 

B 

.6068 

1648.0 

d. 

D 

.5432 

1840.9 

m. 

D' 

.4965 

2014.2 

V8. 

C 

.6028 

1659.0 

d. 

D' 

.5422 

1844.3 

m. 

7' 

E 

.4949 

2020.8 

B. 

C' 

.6007 

1664 . 8 

d. 

E 

.5404 

1850.6 

s. 

F 

.4931 

2028.0 

B. 

D 

.5978 

1672 . 8 

d. 

5 

F 

.5383 

1857.8 

m. 

F' 

.4917 

2033.6 

vvd. 

3 

E 

.5948 

1681.1 

8. 

F' 

.5371 

1862.0 

\vd. 

G 

.4900 

2040.9 

d. 

F 

.5924 

1688.0 

m. 

Gi 

.5359 

1866.0 

vvd. 

G' 

.4891 

2044.5 

vd. 

G 

.5898 

1695.5 

vd. 

G 

.5345 

1871.0 

vd. 

H 

.4874 

2051.5 

m. 

G' 

.5875 

1702.0 

vvd. 

G' 

.5332 

1875.5 

vd. 

I 

.4844 

2064.3 

vd. 

H 

.5846 

1710.5 

d. 

H 

.5313 

1882.0 

m. 

. 

I 

.5805 

1722.5 

m. 

I 

.5283 

1893.0 

vd. 

Bi 

.4821 

2074.1 

vd. 

* 

r 

.5269 

1897.8 

vd. 

C 

.4796 

2085.1 

8. 

B 

.5782 

1729.5 

d. 

" 

C' 

.4787 

2089.2 

d. 

B' 

.5764 

1735.0 

d. 

B 

.5249 

1905.0 

vd. 

8^ 

D 

.4769 

2097.0 

8. 

C 

.5731 

1744.9 

m. 

B' 

.5242 

1907.5 

wd. 

D' 

.4762 

2100.0 

B. 

C' 

.5717 

1749.0 

m. 

c 

'.5221 

1915.3 

8. 

E 

.4734 

2112.5 

m. 

D 

.5693 

1756.5 

m. 

C' 

.5210 

1919.3 

m. 

G 

.4707 

2124.6 

vvd. 

D' 

.5687 

1758.5 

m. 

D 

.5191 

1926.3 

8. 

4 

E 

.5662 

1766.1 

8. 

6 

D' 

.5182 

1929.9 

m. 

F 

.5642 

1772.5 

m. 

E 

.5166 

1935.6 

vs. 

F' 

.5625 

1777.8 

vvd. 

F 

.5148 

1942.5 

vs. 

Gi 

.5614 

1781.4 

vvd. 

G 

.5115 

1955.0 

vd. 

G 

.5599 

1785.9 

vd. 

G' 

.5099 

1961.0 

vd. 

G' 

.5590 

1789.0 

vd. 

H 

.5083 

1967.5 

m. 

H 

.5565 

1796.9 

m. 

I 

.5048 

1980.8 

d. 

_ 

I 

.5529 

1808.6 

d. 

154 


FLUORESCENCE   OF  THE   URANYL   SALTS. 

Table  60. — Magnesium  uranyl  acetate. 


Group 

Group 

Group 

and 

M 

1/mX10' 

Int. 

and 

A* 

1/axX103 

Int. 

and 

/* 

1/mX103 

Int. 

senes. 

series. 

senes. 

2  I 

0.6147 

1627.0 

m. 

[A 

0.5537 

1806.1 

d. 

'A 

0.5063 

1975.1 

vvd. 

B 

.5507 

1815.9 

d. 

B 

.5036 

1985.8 

m. 

[A 

.6115 

1635.4 

m. 

C 

.5475 

1826.5 

m. 

C 

.5007 

1997.1 

m. 

B 

.6072 

1647.0 

vd. 

5 

D 

.5447 

1836.0 

vs. 

7' 

D 

.4983 

2006.8 

m. 

D 

.6002 

1666.1 

m. 

E 

.5423 

1844.0 

s. 

E 

.4966 

2013.8 

s. 

3^ 

E 

.5971 

1674.8 

d. 

F 

.5408 

1879.0 

vvd. 

F 

.4951 

2019.6 

vd. 

G 

.5926 

1687.6 

vd. 

G 

.5382 

1858.0 

d. 

G 

.4929 

2028.7 

d. 

H 

.5897 

1695.7 

vd. 

H 

.5358 

1866.5 

d. 

H 

.4908 

2037.4 

d. 

I 

.5831 

1715.0 

m. 

A 

.5289 

1890.8 

vd. 

B 

.4828 

2071.4 

fA 

.5810 

1721.2 

d. 

B 

.5261 

1900.9 

d. 

C 

.4802 

2082.6 

B 

.5774 

1731.8 

vd. 

C 

.5230 

1912.0 

m. 

Di 

.4791 

2087.1 

D 

.5708 

1751.8 

s. 

6 

D 

.5206 

1920.9 

s. 

8 

E 

.4764 

2099.0 

m.fl 

4 

E 

.5684 

1759.2 

m. 

E 

.5184 

1928.9 

d. 

F 

.4754 

2103.6 

d.l 

F 

.5672 

1763.2 

vd. 

F 

.5170 

1934.4 

vd. 

G 

.4733 

2112.6 

d.1 

G 

.5640 

1773.1 

vd. 

G 

.5145 

1943 . 8 

d. 

H 

.4707 

2124.5 

d.' 

H 

.5613 

1781.6 

d. 

H 

.5128 

1950.1 

d. 

[l 

.^556 

1799.8 

d. 

Table  61. 

— Ammonium  uranyl  acetaie. 

fA 

0.6097 

1640.2 

m. 

[B 

0.5520 

1811.5 

d. 

fB 

0.5048 

1981.0 

d. 

C 

.6044 

1654.5 

vd. 

C 

.5484 

1823.5 

m. 

C 

.5020 

1992.0 

m. 

3 

E 

.5970 

1675.5 

m. 

D' 

.5453 

1834.0 

m. 

D' 

.4994 

2002.5 

8. 

F 

.5945 

1682.0 

d. 

5 

E 

.5424 

1843.5 

s. 

7 

D" 

.4983 

2007.0 

S. 

I 

.5867 

1704.5 

F 

.5404 

1850.5 

m. 

E 

.4970 

2012.0 

s. 

G 

.5379 

1859.2 

vd. 

F 

.4953 

2019.0 

s. 

[B 

.5789 

1727.5 

vd. 

H 

.5360 

1865.5 

vd. 

G 

.4929 

2029.0 

d. 

C 

.5749 

1739.3 

d. 

I 

.5338 

1873.5 

d. 

I 

.4897 

2042.0 

d. 

D' 

.5709 

1751.5 

d. 

4 

E 

.5681 

1760.3 

d. 

B 

.5271 

1897.0 

vd. 

C 

.4816 

2076.5 

m. 

F 

.5661 

1766.5 

m. 

C 

.5242 

1907.5 

m. 

8  D' 

.4787 

2089.0 

vs. 

H 

.5613 

1781.5 

d. 

D' 

.5212 

1918.5 

m. 

ID" 

.4778 

2093.0 

vs. 

I 

.5589 

1789.2 

vd. 

D" 

.5200 

1923.0 

m. 

F 

.4756 

2102.5 

m. 

6^ 

E 
F 
G 
H 

I 

.5189 
.5171 
.5142 
.5127 
.5105 

1927  .-0 
1934.0 
1944.8 
1950.5 
1958.9 

s. 
m. 
vd. 
vd. 

d. 

Table  62 

\ — Potassium  uranyl  acetate. 

fA 

0.6009 

1641.2 

m. 

fB 

0.5512 

1814.2 

vd. 

fB 

0.5041 

1983.9 

vvd. 

C 

.5975 

1673.7 

d. 

C 

.5484 

1823.4 

m. 

C 

.5016 

1993 . 8 

s. 

3 

E 

.5958 

1673.5 

m. 

D 

.5444 

1837.0 

m. 

D 

.4986 

2005.7 

&. 

F 

.5936 

1684.7 

d. 

5 

E 

.5420 

1845.0 

8. 

7< 

E 

.4967 

2013.3 

s. 

H 

.5858 

1707.8 

vd. 

F 

.5399 

1852.2 

m. 

F 

.4948 

2021.0 

vs. 

H 

.5330 

1876.0 

d. 

G 

.4923 

2031.3 

d. 

fc 

.5738 

1742.8 

d. 

G' 

2036.7 

d. 

D 

.5701 

1754.0 

d. 

B 

.5262 

1900.3 

vd. 

H 

.4891 

2044.7 

d. 

4^ 

E 

.5677 

1761.5 

m. 

C 

.5237 

1909.3 

m. 

F 

.5652 

1769.1 

d. 

D 

.5202 

1922.3 

m. 

fc 

.4811 

2078.9 

s. 

G' 

.5614 

1781.3 

vd. 

6 

E 

.5182 

1929.6 

s. 

IF 

.4781 

2091.5 

8. 

H 

.5582 

1791.3 

d. 

F 

.5163 

1937.0 

s. 

.4749 

2105.9 

8. 

G 

.5138 

1946.3 

vd. 

G 

.4724 

2116.8 

vd. 

G' 

.5121 

1952.7 

vd. 

IH 

.5101 

1960.4 

d. 

THE   ACETATES. 
Table  63. — Calcium  uranyl  acetate. 


155 


Group 

Group 

Group 

and 

M 

1//XX103 

Int. 

and 

M 

1//XX103 

Int. 

and 

M 

I/axXIO' 

Int. 

senes. 

senes. 

senes. 

fc 

0.6017 

1662.0 

d. 

fC' 

0.5483 

1823.8 

d. 

fC' 

0.5017 

1993.2 

m. 

D 

.5987 

1670.3 

vvd. 

D 

.5451 

1834.5 

m. 

D 

.4990 

2004.0 

m. 

3 

E 

.5968 

1675.6 

d. 

5 

E 

.5427 

1842.6 

8, 

E 

.4970 

2012.1 

s. 

F 

.5939 

1683.8 

vd. 

F 

.5403 

1850.8 

m. 

7 

F 

.4953 

2019.0 

8. 

H 

.5869 

1703.9 

vd. 

G" 

.5361 

1865.3 

d. 

G" 

.4918 

2033.3 

d. 

J 

.5821 

1717.9 

d. 

H 

.5339 

1873.0 

d. 

H 

.4895 

2042.9 

d. 

I 

.4852 

2051.0 

wd. 

C 

.5740 

1742.2 

d. 

C 

.5240 

1908.4 

m. 

D 

.5703 

1753.5 

d. 

D 

.5212 

1918.6 

m. 

C 

.4875 

2076.8 

m. 

4 

E 

.5682 

1759.9 

m. 

E 

.5190 

1926.8 

s. 

8  D 

.4790 

2087.7 

m. 

F 

.5659 

1767.1 

d. 

6 

F 

.5169 

1934.6 

m. 

F 

.4755 

2103.0 

8. 

G" 

.5612 

1781.9 

vd. 

G" 

.5130 

1949.3 

d. 

G 

.4729 

2114.6 

vd. 

H 

.5590 

1788.9 

vd. 

H 

.5107 

1958.1 

d. 

[k 

.5059 

1976.7 

wd. 

Table  64. 

—Manganese  uranyl  acetate. 

4° 

0.5718 

1748.9 

vd. 

fc 

0.5240 

1908.4 

d. 

fc 

0.4812 

2078.1 

m. 

.5692 

1757.0 

vd. 

D 

.5213 

1918.4 

m. 

8JD 

.4786- 

2089.4 

m. 

6 

E 

.5187 

1927.9 

8. 

F 

.4751 

2104.8 

m. 

C 

.5491 

1821.0 

vd. 

F 

.5168 

1935.0 

8. 

D 

.5454 

1833.5 

vd. 

H 

.5108 

1957.9 

d. 

6 

E 

.5428 

1842.3 

m. 

' 

F 

.5408 

1849.1 

m. 

C 

.5018 

1992.8 

m. 

H 

.5339 

1873.0 

vd. 

D 

.4994 

2002.6 

8. 

7' 

E 

.4971 

2011.7 

8. 

F 

.4952 

2019.4 

8. 

G 

.4936 

2025.9 

vd. 

[h 

.4895 

2042.9 

vd. 

Table  65. — Zinc  uranyl  acetate. 

2  E 

0.6288 

1590.3 

d. 

fD 

0.5460 

1831.6 

vd. 

fA 

0.5050 

1980.3 

wd. 

D' 

.5449 

1835.0 

d. 

C 

.5026 

1989.7 

m. 

A 

.6234 

1640.0 

vd. 

E 

.5430 

1841.6 

s. 

C 

.5011 

1995.8 

m. 

C 

.6045 

1654.3 

vd. 

E' 

.5420 

1845.0 

m. 

D 

.4998 

2000.9 

d. 

E' 

.5967 

1675.8 

m. 

5 

F 

.5411 

1848.0 

m. 

D' 

.4988 

2004.9 

s. 

3 

F 

.5942 

1682.9 

d. 

F' 

.5400 

1851.9 

m. 

E 

.4977 

2009.1 

8. 

G 

.5921 

1689.0 

vd. 

G 

.5382 

1858.0 

vd. 

7i 

E' 

.4965 

2014.0 

m. 

H 

.5893 

1697.0 

vvd. 

H 

.5362 

1865.0 

vd. 

F 

.4957 

2017.2 

s. 

I 

.5870 

1703 . 6 

vd. 

I 

.5342 

1872.0 

m. 

F' 

.4946 

2021.9 

8. 

J 

.5331 

1875.9 

d. 

G 

.4935 

2026.3 

vd. 

A 

.5800 

1724.0 

d. 

H 

.4918 

2033.4 

vd. 

B 

.5780 

1730.1 

vd. 

A 

.5275 

1895.7 

vd. 

I 

.4899 

2041.4 

d. 

C 

.5749 

1739.3 

d. 

C 

.5249 

1905.0 

d. 

J 

.4888 

2045.9 

d. 

E 

.5701 

1754.0 

d. 

C 

.5238 

1909.1 

d. 

' 

4 

E' 

.5685 

1759.0 

8. 

D 

.5219 

1916.1 

d. 

A 

.4843 

2064.8 

vd. 

F 

.5661 

1766.6 

m. 

D' 

.5209 

1919.9 

m. 

C 

.4819 

2075.1 

m. 

G 

.5640 

1773.1 

vd. 

6 

E 

.5193 

1925.6 

8. 

a 

.4809 

2079.6 

m. 

H 

.5624 

1780.6 

vvd. 

E' 

.5182 

1929.9 

m. 

8< 

D 

.4795 

2085.5 

m. 

I 

.5618 

1788.0 

d. 

F 

.5171 

1934.0 

m. 

D' 

.4786 

2089.3 

s. 

F' 

.5160 

1938.0 

m. 

E 

.4776 

2094.0 

m. 

'A 

.5528 

1809.0 

d. 

G 

.5149 

1942.0 

vvd. 

F 

.4758 

2101.9 

8. 

6  B 

.5512 

1814.1 

vd. 

H 

.5131 

1949.1 

wd. 

G, 

.4746 

2107.0 

d. 

ic 

.5482 

1824.0 

m. 

I 
J 

.5110 
.5099 

1956.9 
1961.3 

d. 
d. 

156 

FLUORESCENCE   OF  THE   URANYL 

SALTS. 

Table  66 

. — Rubidium  uranyl  acetate 

Group 

Group 

Group 

and 

M 

l//iX10» 

Int. 

and 

M 

1//XX103 

Int. 

and 

M 

l//iXlO» 

Int. 

senes. 

senes. 

senes. 

fB 

0.6093 

1641.2 

vd. 

fc 

0.5489 

1821.8 

s. 

fi[H 

0.5129 

1949.7 

vd. 

.5977 

1673.1 

s. 

C 

.5476 

1826.2 

vd. 

^\I 

.5109 

1957.3 

m. 

.5955 

1679.3 

d. 

D 

.5458 

1832.3 

m. 

H 

.5879 

1701.0 

wd. 

5- 

D' 

.5445 

1836.5 

d. 

C 

.5022 

1991.2 

8. 

E 

.5428 

1842.3 

vs. 

D 

.4995 

2002.0 

8. 

A' 

.5811 

1720.9 

vd. 

F 

.5405 

1850.0 

s. 

D' 

.4984 

2006.4 

m. 

C 

.5753 

1738.2 

m. 

G 

.5377 

1859.8 

vd. 

7' 

E 

.4971 

2011.7 

8. 

C 

.5739 

1742.5 

wd. 

H 

.5360 

1865.7 

vd. 

F 

.4953 

2019.0 

3. 

D 

.5717 

1749.2 

d. 

I 

.5338 

1873.4 

s. 

G 

.4927 

2029.6 

wd. 

4J 

D' 

.6703 

1753.3 

d. 

H 

.4916 

2034.2 

wd. 

E 

.5685 

1759.0 

vs. 

c 

.5241 

1908.0 

s. 

I 

.4893 

2043.7 

m. 

F 

.5662 

1766.2 

s. 

C 

.5229 

1912.4 

wd. 

' 

G 

.5639 

1773.4 

wd. 

D 

.5214 

1917.9 

s. 

c 

.4813 

2077.7 

8. 

H 

.5618 

1780.0 

wd. 

6 

D' 

.5202 

1922.0 

m. 

D 

.4790 

2087.7 

8. 

I 

.6592 

1788.3 

m. 

E 

.5188 

1927.5 

vs. 

8^ 

D' 

.4780 

2092.1 

m. 

F 

.5170 

1934.2 

s. 

F 

.4751 

2104.8 

8. 

.5554 
.5525 

1800.6 
1810.0 

d. 
d. 

[o 

.5144 

1944.0 

vd. 

IG 

.4730 

2114.2 

vd. 

Table  67. — Strontium  uranyl  acetate. 


2  I 

I 


0.6112 

.5974 
.5951 
.5872 
.5812 

.5752 
.5721 
.5687 
.5663 
.5616 
.6589 


1636.1 

d. 

c 

D 

0.5483 
.5453 

1674.0 

na. 

E 

.5427 

1680.5 

m. 

5 

F 

.5407 

1703.0 

d. 

G 

.5363 

1720.7 

d. 

H 

I 

.6334 
.5300 

1738.6 

d. 

1747.9 

d. 

c 

.5239 

1768.5 

m. 

D 

.5211 

1765.8 

m. 

E 

.5187 

1780.8 

vd. 

6^ 

F 

.5169 

1789.1 

vd. 

G 
H 

I 

.5131 
.6104 
.5078 

1823.9 

m. 

[c 

0.5017 

1834.0 

vd. 

D 

.4990 

1842.6 

m. 

7' 

E 

.4969 

1849.4 

m. 

F 

.4950 

1864.5 

d. 

G 

.4916 

1874.9 

d. 

H 

.4888 

1886.8 

vd. 

fc 

.4812 

1908.6 

m. 

8{D 

.4789 

1919.0 

d. 

F 

.4751 

1928.0 

s. 

1934.5 

s. 

1949.0 

d. 

1959.1 

d. 

1969.4 

d. 

1993.2 
2004.0 
2012.5 
2020.4 
2034.0 
2046.9 

2078.2 
2088.1 
2106.0 


Table  68. — Silver  uranyl  acetate. 

fE' 

0.5979 

1672.6 

d. 

^c 

0.5500 

1818.4 

d. 

fc 

0.5027 

1989.2 

d. 

3F 

.5961 

1677.6 

vd. 

D 

.5465 

1829.7 

m. 

D 

.5000 

2000.2 

8. 

Ih 

.5878 

1701.2 

vd. 

6 

E 

.5437 

1839.4 

8. 

7 

E 

.4979 

2008.6 

m. 

F 

.6417 

1846.0 

m. 

F 

.4960 

2016.1 

8. 

A 

.5806 

1722.6 

vd. 

G 

.5379 

1859.0 

vd. 

G 

.4930 

2028.6 

vd. 

c 

.5764 

1736.0 

d. 

H 

.6346 

1871.0 

vd. 

H 

.4902 

2040.0 

vd. 

D 

.5730 

1745.1 

d. 

* 

4 

E 

.5699 

1754.7 

m. 

fc 

.6250 

1904.9 

d. 

C 

.4824 

2073.0 

d. 

F 

.6678 

1761.1 

d. 

D 

.6227 

1913.2 

m. 

8{D 

.4796 

2085.1 

8. 

G' 

.6625 

1777.7 

vd. 

6 

E 

.5198 

1923.9 

s. 

F 

.4769 

2101.6 

m. 

H 

.5600 

1786.7 

vd. 

F 

.5183 

1931.0 

m. 

G 

.5141 

1945.1 

vd. 

[h 

.5113 

1965.7 

vd. 

THE  ACETATES. 

Table  69. — Barium  wranyl  acetate. 


157 


Group 

Group 

Group 

and 

A* 

l//iX10» 

Int. 

and 

-M 

1//XX103 

Int. 

and 

M 

I/mXIO' 

Int. 

senes. 

senes. 

senes. 

\C 

0.6055 

1651.5 

vd. 

fc 

0.5498 

1818.8 

d. 

fc 

0.5025 

1990.0 

d. 

E 

.5993 

1668.6 

d. 

D 

.5471 

1827.8 

d. 

D 

.5000 

2000.0 

m. 

3 

F 

.5963 

1677.0 

d. 

5 

E 

.5441 

1837.9 

s. 

7' 

E 

.4978 

2008.8 

m. 

G 

.5923 

1688.3 

vd. 

F 

.5415 

1846.7 

s. 

F 

.4959 

2016.5 

8. 

t 

H 

.5888 

1698.4 

d. 

G 

.5387 

1856.3 

d. 

G 

.4933 

2027.2 

vd. 

H 

.5349 

1869.5 

d. 

H 

.4901 

2024.4 

d. 

C 

.5764 

1734.9 

vd. 

D 

.5733 

1744.3 

d. 

C 

.5250 

1904.8 

d. 

C 

.4878 

2075.5 

m. 

4 

E 

.5700 

1754.4 

m. 

D 

.5226 

1913.5 

m. 

«te 

.4795 

2085.5 

8. 

F 

.5672 

1763.0 

m. 

6 

E 

.5201 

1922.7 

s. 

.4759 

2101.3 

m. 

G 

.5638 

1773.7 

d. 

F 

.5180 

1930.5 

s. 

G 

.4731 

2113.7 

vd. 

H 

.5602 

1785.1 

d. 

G 

.5150 

1941.7 

vd. 

[h 

.5116 

1954.7 

d. 

Table  70. — Lead  uranyl  acetate. 

2  K 

0.6202 

1621.6 

m. 

fc 

0.5489 

1821.9 

m. 

fi/l 

0.5100 

1960.8 

vd. 

C' 

.5472 

1827.5 

m. 

% 

.5089 

1965.0 

vd. 

B 

.6086 

1643.1 

vd. 

D 

.5459 

1831.7 

8. 

C 

.6048 

1653.4 

vd. 

E 

.5439 

1838.7 

S. 

fB 

.5042 

1983.5 

m. 

D 

.6015 

1662.5 

m. 

E' 

.5423 

1844.0 

vd. 

Ci 

.5028 

1989.0 

vd. 

E 

.5991 

1669.1 

m. 

5 

F 

.5410 

1848.3 

vd. 

C 

.5019 

1992.4 

8. 

3 

G 

.5938 

1684.1 

vd. 

G 

.5390 

1855.1 

d. 

C' 

.5008 

1997.0 

8. 

I 

.5909 

1692.4 

d. 

H 

.5369 

1862.4 

m. 

D 

.4996 

2001.8 

8. 

H' 

.5891 

1697.5 

vd. 

H' 

.5352 

1868.5 

d. 

7- 

El 

.4983 

2006.8 

wd. 

I 

.5859 

1706.8 

m. 

I 

.5333 

1875.1 

vd. 

E 

.4976 

2009.6 

vat. 

L 

.5841 

1712.1 

d. 

L 

.5320 

1879.6 

vd. 

F 

.4948 

2021 . 1 

vd. 

: 

" 

G 

.4936 

2025.8 

vd. 

B 

.5788 

1727.7 

d. 

B 

.5269 

1897.8 

m. 

H 

.4916 

2034.0 

m. 

C 

.5751 

1738.7 

d. 

Ci 

.5252 

1904.0 

vd. 

I 

.4886 

2046.7 

vd. 

C' 

.5741 

1741.8 

d. 

C 

.5242 

1907.6 

S. 

D 

.5722 

1747.7 

s. 

C' 

.5230 

1911.9 

8. 

fB 

.4837 

2067.4 

m. 

4 

E 

.5700 

1754.3 

s. 

D 

.5219 

1916.2 

VS. 

Ci 

.4824 

2073.0 

vd. 

G 

.5649 

1770.1 

d. 

6 

El 

.5201 

1922.7 

vd. 

C 

.4814 

2077.4 

8. 

H 

.5621 

1778.9 

m. 

E 

.5195 

1925.0 

vs. 

8< 

D 

.4790 

2087.5 

8. 

H' 

.5611 

1782.3 

d. 

E' 

.5186 

1928.3 

vd. 

E 

.4772 

2095.7 

8. 

I 

.5591 

1788.7 

vd. 

F 

.5172 

1935.0 

vd. 

E' 

.4766 

2098.2 

wd. 

L 

.5567 

1796.3 

d. 

G 

.5149 

1942.1 

d. 

F 

.4749 

2105.9 

d. 

H 

.5130 

1949.1 

m. 

G 

.4737 

2111.0 

vd. 

^c 

.5518 
.5500 

1812.1 
1818.2 

m. 
vd. 

H' 

.5119 

1953.4 

vd. 

158 


FLUORESCENCE    OF  THE    URANYL   SALTS. 
Table  71. — Lithium  uranyl  acetate. 


Series. 

Group 
2. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

A. 

1638.0 
1657.4 

c 

1742.1 
1751.0 
1760.5 
1769.0 

1824.5 
1834.4 
1844.0 
1852.0 

1909.0 
1919.8 
1928.9 
1935.8 

1993.7 
2005.1 
2013.1 
2021 . 1 

2080.0 
2090.5 



"2i64!8' 

84.52 
84.89 
84.03 
84.05 

D 

E 

1677.0 

F      

F' 

G 

1864.7 
1874.1 

1950.2 
1960.2 

85.50 
84.65 

H 

1707.0 

1789.0 

2045.6 

Gen.  av 

84.50 

Table  72. — Sodium  uranyl  acetate. 

Bi 

1643.5 
1648. C 

1729.5 
1735.0 

1815.0 
1820.2 

2074.1 

86.12 
86.43 

B 

1905.0 
1907.5 
1915.3 
1919.3 
1926.3 
1929.9 
1935.6 
1942.5 

1989.2 

B' 

c 

1659.0 
1664.8 
1672.8 

1744.9 
1749.0 
1756.5 
1758.5 
1766.1 
1772.5 
1777.8 
1781.4 
1785.9 
1789.0 
1796.9 
1808.6 

1828.8 
1834.1 
1840.9 
1844.3 
1850.6 
1857.8 
1862.0 
1866.0 
1871.0 
1875.5 
1882.0 
1898.0 
1897.8 

2001.0 
2004.9 
2011.3 
2014.2 
2020.8 
2028.0 
2033.6 

2085.1 
2089.2 
2097.0 
2100.0 

iiiiis' 

85.22 
84.88 
84.84 
85.37 
84.76 
84.90 
85.27 
85.25 
84.50 
85.17 
85.20 
85.36 

C' 

D 

D' 

E 

1597.0 

1681 . 1 
1688.0 

F 

F' 

Gi 

1695.5 
1702.0 

G 

1955.0 
1961.0 
1967.5 
1980.8 

2040.9 
2044.5 
2051.5 
2064.3 

2124.6 

G' 

H 

1710.5 
1722.5 

I 

1637.6 

F 

Gen.  av 

85.22 

Table  73. — Magnesium  uranyl  acetate. 


A 

1635.4 
1647.0 

1721.2 
1731.8 

1806.1 
1815.9 
1826.5 

1890.8 
1900.9 
1912  0 

1975.1 
1985 . 8 
1997.1 

2071.4 
2082.6 
2087.1 

'2699  .'6' 

2103.6 
2112.6 
2124.6 

84.93 
84.88 
85.37 

B 

C 

C' 

D 

1666.1 
1674.8 

1751.8 
1759.2 
1763.2 
1773.1 
1781.6 
1799.8 

1836.0 
1844.0 
1849.0 
1858.0 
1866.5 

1920.9 
1928.9 
1934.4 
1943.8 
1950.1 

2006.8 
2013.8 
2019.6 
2028.7 
2037.4 

85.18 
84.84 
85.10 
85.00 
85.76 
86.40 

E 

F 

G 

1687.6 
1695.7 
1715.0 

H 

I 

1627.0 

Gen.  av 

85.19 

Table  74. — Ammonium  uranyl  acetate. 


A 

1640.2 

B 

1727.5 
1739.3 
1751.5 

1811.6 
1823.6 
1834.0 

1897.0 
1907.5 
1918.5 
1923.0 
1927.0 
1934.0 
1944.8 
1950.5 
1968.9 

1981.0 
1992.0 
2002.5 
2007.0 
2012.0 
2019.0 
2029.0 

2076.5 
2089.0 
2093.0 

*2i62!5' 

84.50 
84.40 
84.38 
86.00 
84.13 
84.10 
84.90 
84.60 
84.38 

C 

1654.5 

D 

D" 

E 

1675.5 
1682.0 

1760.3 
1766.6 

1843.6 
1860.5 
1859.2 
1865.5 
1873.5 

F 

G 

H 

1781.6 
1789.2 

I 



1704.5 

2042.0 

Gen.  av .  ,  . . 

84.40 

THE   ACETATES. 
Table  75. — Potassium  uranyl  acetate. 


159 


Series. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 
8. 

Average 
interval. 

A 

1641.2 

B 

1814.2 
1823.4 
1837.0 
1845.0 
1852.2 

1900.3 
1909.3 
1922.3 
1929.6 
1937.0 
1946.3 
1952.7 
1960.4 

1983.9 
1993.8 
2005.7 
2013.3 
2021.0 
2031.3 
2036.7 
2044.7 

'2678!9* 
2091.5 

iiosio" 

2116.8 

84.83 
84.56 
84.63 
84.95 
84.24 
85.25 
85.13 
84.26 

c 

1656.1 

1742.8 
1754.0 
1761.5 
1769.1 

D 

E 

1673.5 
1684.7 

F 

G 

G' 

1781.3 
1791.3 

1845.0 
1876.0 

H 

1707.8 

Gen.  av. 

84.57 

Table  76. — Calcium  uranyl  acetate. 

Series. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 
7. 

Group 

8. 

Average 
interval. 

c 

1742.2 

1823.8 

1908.4 

1993.2 

2076.8 

83.87 

C' 

D 

1662.0 
1670.3 
1675.6 
1683.8 

1753.5 
1759.9 
1767.1 

1834.5 
1842.6 
1850.8 

1918.6 
1926.8 
1934.6 

2004.0 
2012.1 
2019.0 

2087.7 

2103.0 
2114.6 

83.91 
84.12 
83.85 

E 

F 

G' 

G" 

1781.9 
1788.9 

1865.3 
1873.0 

1949.3 
1958.1 

2033.3 
2042.9 
2051.0 

83.80 
84.66 

H 

1703.9 

I 

J 

1717.9 

Ki 

1976.7 

Gen.  av. 

83.88 

Table  77.— 

-Mangam 

se  uranyl  acetate. 

Series. 

Group 
3. 

Group 

4. 

Group 
5. 

Group 
6. 

Group 
7. 

Group 

8. 

Average 
interval. 

c 

1821.0 
1833.5 
1842.3 
1849.1 

1908.4 
1918.4 
1927.9 
1935.0 

1992.8 
2002.6 
2011.7 
2019.4 
2025.9 
2042.9 

2078.1 
2089.4 

2i64!8' 

85.70 
85.12 
84.90 
85.23 

D 

1748.9 
1757.0 

E 

F 

Gi 

H 

1873.0 

1957.9 

84.95 

Gen.  av. . 

85.19 

160 


FLUORESCENCE    OF   THE    URANYL    SALTS. 

Table  78. — Zinc  uranyl  acetate. 


Series. 

Group 
2. 

Group 
3. 

Group 

4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

A 

1640.0 

1724.0 
1730.1 

1809.0 
1814.1 

1895.7 

1980.3 

2064.8 

84.96 
'84.00 
84.16 
85.03 
84.48 
84.77 
83.95 
85.22 
83.80 
85.00 

B 

c 

1654.3 

1905.0 
1909.1 
1916.1 
1919.9 
1925.6 
1929.9 
1934.0 
1938.0 

1989.7 
1995.8 
2000.9 
2004.9 
2009.1 
2014.0 
2017.2 
2021.9 

2075.1 
2079.6 
2085.5 
2089.3 
2094.0 
2101.9 

'2167.0' 

c 

1739.6 

1824.0 
1831.6 
1835.0 
1841.6 
1845.0 
1848.0 
1851.9 

D 

D' 

E 

1590.3 

1675  is" 
1682.9 

1754.0 
1759.0 
1766.6 

E' 

F 

F' 

Gi 

G 

1689.0 
1697.0 
1703.6 

1773.1 
1780.6 
1788.0 

1858.0 
1865.0 
1872.0 
1875.9 

1942.0 
1949.1 
1956.9 
1961.3 

2026.3 
2033.4 
2041.4 
2045.9 

84.33 
84.20 
84.45 
85.00 

H 

I 

J 

Gen.  av 

84.51 

Table  79. — Rubidium  uranyl  acetate. 


Series. 

Group 
2. 

Group 
3. 

Group 

4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

A 

1800.6 

A' 

1720.9 

"1738  .'2' 
1742.5 
1749.2 
1753.3 
1759.0 
1766.2 
1773.4 
1780.0 

B 

1641.2 

1810.0 
1821.8 
1826.2 
1832.3 
1836.5 
1842.3 
1850.0 
1859.8 
1865.7 

84.40 
84.88 
84.45 
84.62 
84.70 
84.65 
85.10 
85.20 
84.73 

C 

1908.0 
1912.4 
1917.9 
1922.0 
1927.5 
1934.2 
1944.0 
1949.7 

1991.2 

2077.7 

C 

D 

2002.0 
2006.4 
2011.7 
2019.0 
2029.6 
2034.2 

2087.7 
2092.1 

'2i64!8' 
2114.2 

D' 

E 

1673.1 
1679.3 

F 

G 

H 

H' 

1701.0 

I 

1788.3 

1873.4 

1957.3 

2043.7 

85.13 

Gen.  av 

. 

84.86 

Table  80. — Strontium  uranyl  acetate. 


Series. 

Group 
2. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

C 

1738.6 
1749.9 
1758.5 
1765.8 
1780.8 

1823.9 
1834.0 
1842.6 
1849.4 
1864.5 

1908.6 
1919.0 
1928.0 
1934.5 
1949.0 

1993.2 
2004.0 
2012.5 
2020.4 
2034.0 

2078.2 
2088.1 

"2165.6" 

84.90 
85.05 
84.63 
84.90 
84.40 

D 

E 

1674.0 
1680.5 

F 

G 

Hi 

1703.0 

H 

1789.1 

1874.9 
1886.8 

1959.1 
1669.4 

2045.9 



85.60 
83.32 

I 

1636.1 

1720.7 

Gen.  av 

84.74 

THE   ACETATES. 
Table  81. — Silver  uranyl  acetate. 


161 


Series. 

Group 

2. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 
7. 

Group 

8. 

Average 
interval. 

A 

1722.5 
1735.0 
1745.1 
1754.7 

c 

1818.4 
1829.7 
1839.4 

1904.9 
1913.2 
1923.9 

1989.2 
2002.2 
2008.6 

2073.0 
2085.1 

84.50 
85.00 
84.63 

D        

E 

E' 

1672.5 
1671.5 

F.. :...:..... 

1761.1 

1846.0 
1859.0 

1931.0 
1945.1 

2016.1 
2028.6 

2101.5 

84.80 
84.80 

G 

G' 

1777.7 
1785.7 

H 

1701.2 

1871.0 

1955.7 

2040.0 



84.70 

Gen.  av . . . . 

84.74 

Table  82. — Barium  uranyl  acetate 

Series. 

Group 
2. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 

8. 

Average 
interval. 

c 

1651.5 

1734.9 
1744.3 
1754.4 
1763.0 
1773.7 
1785.1 

1818.8 
1827.8 
1837.9 
1846.7 
1856.3 
1869.5 

1904.8 
1913.5 
1922.7 
1930.5 
1941.7 
1954.7 

1990.0 
2000.0 
2008.8 
2016.5 
2027.2 
2040.4 

2075.5 
2085.5 

'2161.3' 
2113.7 



84.80 
85.30 
85.05 
84.86 
85.08 
85.50 

D 

E 

1668.6 
1677.0 
1688.3 
1698.4 

F 

G 

H 

Gen.  av.  , . . 

85.08 

Table  83. — Lead  uranyl  acetate. 


Series. 

Group 
2. 

Group 
3. 

Group 
4. 

Group 
5. 

Group 
6. 

Group 

7. 

Group 
8. 

Average 
interval. 

B 

1643.1 

1727.7 

1812.1 
1818.2 
1821.9 
1827.5 
1831.7 

1897.8 
1904.0 
1907.6 
1911.9 
1916.2 
1922.7 
1925.0 
1928.3 
1935.0 
1942.1 
1949.1 
1953.4 
1960.8 

1983.5 
1989.0 
1992.4 
1997.0 
2001.8 
2006.8 
2009.6 

'2621!!' 
2025.8 
2034.0 

2067.4 
2073.0 
2077.4 

2087.5 

'2695  .'7' 
2098.2 
2105.9 
2111.0 

84.86 
84.93 
84.75 
85.07 
85.00 
84.10 
85.32 
84.30 
84.40 
85.38 
85.40 
85.30 
85.02 

Ci 

C 

1653.4 

1738.7 
1741.8 
1747.7 

C' 

D 

1662.5 

El 

E 

1669.1 

1754.3 

1838.7 
1844.0 
1848.3 
1855.1 
1862.4 
1868.5 
1875.1 

E' 

F 

G 

1684.1 
1692.4 
1697.5 
1706.8 

1770.1 
1778.9 
1782.3 
1788.7 
1796.3 

H 

H' 

I 

1621.6 

2046.7 



L 

Gen.  av 

85.12 

162  FLUORESCENCE   OF  THE   URANYL   SALTS. 

Table  84. — Summary  of  average  intervals  of  the  double  acetates. 


Substance. 

Interval. 

Substance. 

Interval. 

Li(U02)(C2H802)3.3H20 

Na(U02)(C2HsOi)« 

84.50 
85.22 
85.19 
84.40 
84.57 
83.88 
85.19 

Zn(U02)2(C2H302)6.7H20 

Rb(U02)(C2Hs02)a 

84.51 
84.86 
84.74 
84.74 
85.08 
85.12 

Mg(U02)2(C2H802)«.7H20.  .  . . 
NH4(U02)(C2H802)8 

Sr(U02)2(C2H302)6.6H20 

Ag(U02)(C2H302)8 

KdJOsKCsHaOo)^         

Ba(U02)  (C2H302)6 .  6H2O 

Pb(U02)(C2H802)4.4H20 

General  average 

Ca(U02)2(C2H302)o.8H20 

Mn(U02)(C2H,02)4.6H20 

84.76 

Absorption  Spectra  of  the  Acetates. 

The  fluorescence  and  absorption  of  the  acetates  are  related  to  each 
other  in  a  manner  entirely  similar  to  that  already  established  in  the 
case  of  the  other  uranyl  compounds. 

The  absorption  bands  occur  in  series  of  constant  interval  and  this 
interval  is  much  shorter  than  that  pf  the  fluorescence  series.  Fluores- 
cence and  absorption  overlap  in  the  reversing  region,  with  numerous 
coincidences  and  an  interlocking  of  the  fluorescence  and  absorption 
intervals.  Reversals,  both  exact  and  of  the  well-known  displaced  type, 
are  more  frequent,  perhaps,  than  in  any  family  of  uranyl  salts  as  yet 
studied.  A  notable  example  occurs  in  the  spectrum, of  lead  uranyl 
acetate  (see  fig.  86). 


PB. 

Rrv 

^ll<(A 

1 

1 



— 

-  — 

31 

0« 

Fig.  86. 

The  absorption  spectra  fall  into  two  fairly  well  defined  classes : 

(1)  Double  acetates  of  Li,  NH4,  Na,  K,  Ca,  Zn,  Rb,  Sr.,  Ag.,  Ba. 

In  this  class  the  system  of  bands  having  a  series  interval  of  70+ 
ends  at  about  2,180,  where  is  located  the  head  of  the  strongest  series. 

Band  E  of  the  fluorescence  series  is  usually  missing  in  group  8  and  is 
supplanted  by  a  strong  absorption  band  (1)  located  85=±=  frequency 


THE  ACETATES. 


163 


units  from  the  terminating  absorption  band  mentioned  above,  des- 
ignated as  e  in  accordance  with  convention  used  in  previous  papers. 

An  excellent  example  of  this  type  of  change  from  fluorescence  to 
absorption  is  afforded  by  the  spectrum  of  barium  uranyl  acetate 
(fig.  87).  Here  an  exact  reversal  of  band  Eg^  occurs  and  the  strong 
absorption  band  e,  which  takes  the  place  of  E  in  that  group,  is  85 
frequency  units  from  the  first  member  of  the  strong  e  series  which 
extends  toward  the  ultra-violet  with  the  usual  absorption  interval 
of  70  units.  Displaced  reversals  F,  G,  and  H  also  occur — ^an  indica- 
tion of  the  probably  complex  structure  of  these  bands.  The  corre- 
sponding absorption  bands  are  likewise  85  units  from  the  first  members 
of  the/',  g\  and  W  series  of  the  absorption  spectrum. 

There  is  almost  as  notable  a  resemblance  between  the  absorption 
spectra  of  this  class  as  between  their  fluorescence  spectra.  The  resolu- 
tion is,  however,  not  so  good,  and  all  the  members  of  the  various  series 
are  not  so  easily  located.  Almost  without  exception  the  bands  which 
can  be  observed  are  definitely  related,  in  the  manner  just  described, 
to  the  fluorescence  series. 

(2)  The  single  acetates  U02(C2H302)2  and  U02(C2H302)2+2H20; 
double  acetates  of  Mg,  Mn,  Pb. 

Here  the  absorption  system  (interval  70=*=)  distinctly  overlaps  the 
fluorescence  system  extending  into  the  region  of  groups  8  and  7  beyond, 
without  change  of  interval. 


flROUP    7 

r 
f 


6R0UP    8 


GROUP     9 


-•9_ 


.•«. 


f 
£ as 


.70 


.70. 


20  00 


22|00 


Fio.  87. 

The  various  series  of  absorption  bands  located  in  our  visual  and 
photographic  studies  of  the  acetates  are  contained  in  tables  85  to  97 
inclusive.  Frequencies  and  average  intervals  are  given  for  each  salt, 
the  series  being  designated  as  usual  by  small  letters,  which  indicate 
their  relation  to  fluorescence  series  denoted  by  the  corresponding 
capital  letter.  The  three  examples  of  bands  or  series  not  thus  related 
to  visible  fluorescence  are  indicated  by  means  of  the  Greek  letter  7. 

*  This  band  Eg  may  appear  either  as  fluorescence  or  as  absorption  according  to  the  conditions 
of  illumination,  etc.  It  is  commonly  seen  as  fluorescence  in  the  spectrum  of  the  zinc  uranyl 
acetate  and  as  absorption  in  the  spectra  of  othei*  salts  of  this  class. 


^ 


164 


FLUORESCENCE   OF  THE   URANYL   SALTS. 
Table  Sb—Li{U02){C2Hi02)z.SHtO. 


Series. 

Frequencies. 

Interval. 

c 

c' 

e 

e' 

/ 

f" 

Oi 

a 

h 

h' 

2234.5         2375.0         2446.5         2514.8         2584.8         

2085.0         

70.06 

2097.8        2185.0        2256.6        2325.0        2396.2         

2100.0         

70.40 

2026.5         2108.8         

2110.8         

2113.0         

2117.8        2201.5        2623.8         

2124.0         

70.39 

2129.0         

Weighted  average 

70.27 

Table  m.—NH,{U02){C2H^02)z. 

Series. 

Frequencies. 

Interval. 

/Si 

2145.6 

7 

1996.5 

2082.4         2163.4         2299.2         2511.6         

69.62 

c 

2232.4 

2374.0         2446.3         

71.73 

e 

2096.2 

2183.2        2253.8        2322.8        2394.2         

70.12 

/' 

2107.8 

0 

2114.8 



h 

2119.8 

2207.0        2278.8        2348.5        2422.8        2487.5 

70.13 

i' 

2047.8 

2130.0         



W 

eighted  average 

70.19 

Table  87.— Na{U02){C2Hz02h. 


Series. 

Frequencies. 

Interval. 

b 

b' 

c 

di 

d 

«! 

e 

e' 

/ 

/' 

g 

h 

t 

2229.2         

2375.3         

2239.6        2311.1         2382.1         2454.0        2524.0        2591.8 
2093.4         

69.95 

2395.8         

2328.3         2472.8          

2102.6         2190.1         2259.4         2332.1         2403.8         2542.4 

2265.0         2336.4         2409.1         2475.9         

2111.0         2478.9         

70.46 
70.30 

2117.7  2277.4         2343.0         2415.3         

2126.8  2211.4         2285.7         2350.7         2423.7         2569.1 
2137.7         2217.8         2291.0         2358.5         2430.1         2499.4 
2336.3         

70.40 
71.54 
70.15 

Weighted  average 

70.46 

THE   ACETATES. 
Table  SS.—MgiUO^h. {CtHzO^^ . 7H2O. 


165 


Series. 

Frequencies. 

Interval. 

Cl 

c 

c' 

d' 

e 

/ 

a\ 

a 

0' 

2161.0         

2168.3         2239.2         

2172.8         2315.0         

2092.8         

70.90 
71.10 

2182.8         

2102.2          

2108.4          

2266.0         2336.2          

2115.3         2199.3         2269.0         

70.20 
69.70 

Weighted  average 

70.60 

Table  ^^.—K{U02){C2HzOi), 


Series. 

Frequencies. 

Interval. 

c 

c' 

T 

d 

e 

el 

h 

g 

g' 

h 

h' 

2166.0        2234.0         

2084.0         

2000.0         

68.00 

2176.1          

2011.5         

2017.0        2100.0        2186.0        2256.3        2326.5         

2025.0         2109.3          

70.25 

2116.0         2203.0 

2124.0         2211.6         2292.2         2349.0         

2131.8         

2061.8         

68.70 

Weighted  average 

69.18 

Table  90.— Ca(f/02)2(C2iy302)6. 5^20. 


Series. 

Frequencies. 

Interval. 

7 

d 

e 

/ 

/i 

gi 

g 

h' 

^1 

t 

2023.1         2092.5        2166.8         

2173.0  2245.2         2312.7         2384.9         

2180.1  2249.2         2317.5        2390.1         

2104.8         

71.85 
70.63 
70.00 

2185.0  2254.3         2325.6         2395.8         

2198.8         2340.3         2409.6         

2032.1  2115.1         2203.6        2274.3        2415.5         

2123.6         2278.4         2349.1          

2126.3         

70.27 
70.27 
70.63 
70.70 

2436.6         

Weighted  average 

70.54 

Table  ^l.—MniUO^UC^HzO^^.eH^O. 

Series. 

Frequencies. 

Interval. 

c 

e 

e^ 

g 

2425.0         

2011.5        2094.0        2178.4        2236.2        2307.6         

2311.3         

2110.5         2181.2         2251.5          

*7i;62" 
' "76.66" ' 

Weighted  average 

71.25 

166  FLUORESCENCE   OF  THE   URANYL   SALTS. 

Table  '^2.—Zn{UOMC2Hi02)fi.7HiO. 


Series. 

Frequencies. 

Interval. 

c 

e 

r 

a 

h 

h' 

t 

2372.5        2442.6         

2096.4        2181.5        2251.7        2322.9        2392.5         

2188  2           

70.10 
70.10 

2263.0         

2178.6         2343.6         2415.0         

2205.6        2277.9        2350.7         

2129  9               ...          

"7i!46" 
72.80 

Weighted  average 

70.77 

Table  9S.—Rh(U02){C2Hz02)z. 


Series. 

Frequencies. 

Interval. 

a 

&i 

c 

c' 

d' 

d" 

e 

Oi 

g' 

»1 

% 

2059  3         

2070.8         

2158.9        2292.2        2299.4        2373.6        2440.8         

2081.6         

70.27 

2093.8        2246.7        2317.0         

2392  3         

70.35 

2186.7        2259.4        2326.1         2399.8         

2027.2         

71.03 

2115.1         

2041  7                             ...            ...                .                 

2129.0        2209.5        2279.6        2350.2        2423.1         

71.20 

Weighted  average 

70.78 

Table  94.— 5r(?702)2(C2^302)6 •  6H2O. 

Series. 

Frequencies  of  absorption  bands  at  —185'*  (groups  8  to  12). 

Interval. 

ci 

c 

ei 

e 

e' 

e" 

h 

h' 

% 

2371.2         

2375.6         

2390.0         

2094. 5R     2181.4        2251.9         2322.5         

2185.7        2254.1         

2399.9         

70.55 
68.40 

2273.8        2412.7         

2206.0        2347.8         

2209.0        2279.1         2350.0        2420.0        2490.0         

69.45 
70.90 
70.25 

General  weighted  average 

70.11 

Table  Qd.—AgUOiidHzOz). 


Series. 

Frequencies. 

Interval. 

c 

e 

r 

0 

h 

i 

2231.4        2369.7         

2180.0        2251.3        2321.2        2390.1         

2107.0        2191.4         

69.15 
70.03 

2116.0         

2125.0         

2133.0        2204.1         2276.3        2344.7         

70.39 

Weighted  average 

70.01 

THE  ACETATES. 

Table  96.— 5a(C702)2(C2fl'302)6 . eH^O. 


167 


Series. 

Frequencies. 

Interval. 

h 

c 

e 

/' 

Q' 

Oh 

2294.1         

2227.2  2370.8          

2094.7         2180.1         2250.2         2322.5         2393.6         

2105.3  2187.2         2260.0         

2115.1         

71.82 
71.13 
72.80 

2204.1         2275.8         2419.0         2486.9         

70.70 

Weighted  average 

71.36 

Table  97.—Pb(U02)iC2H,02)H20. 


Series. 

Frequencies. 

Interval. 

5 

2065.0       

Cl 

2072.0       2142.5 

2355.0       2426.5 

2495.0       

70.5 

c'd 

2365.0       2437.5 

2506.0       

71.5 

e 

2094.5       2236.5 

2309.8       2380.0 

2450.0       2521.0       2594.5 

71.43 

e' 

2098.0       2168.5 

2240.0       2313.5 

71.83 

e" 

2101.5       2389.0 

71.87 

/ 

2105.5       2176.5 

2248.4       2321.5 

2392.5       

71.75 

9 

2110.5        





h 

2119.5        



h' 

2125.0       2194.5 

2264.0       2332.5 

7i.00 

k 

2201.5       2272.0 

2341.0       2413.5 

2482.0       2552.5       

71.00 

Weighted  a 

verage 

71.21 

Table  98. — General  weighted  averages  of  intervals  of  absorption  series  in  the  spectra  of  the 

acetates  at  —185°  C. 


Substance. 

Interval. 

Substance. 

Interval. 

U02(C2H,02)2 

71.04 
72.35 
70.27 
70.19 
70.46 
70.60 
69.18 
70.54 
71.25 

Zn(U02)2(C2H302)6.7H20 

Rb  U02(C2H302)3 

70.77 
70.78 
70.11 
70.01 
71.36 
71.21 

U02(C2H302)2  .  2H2O 

LiU02(C2H302)3.3H20 

NH4U02(C2H302)s 

Sr(U02)2(C2H302)6 .  6H2O 

Ag  U02(C2H302)s 

Na  U02(C2H302)3 

Ba(U02)2(C2H302)6.6H20 

Pb(U02)(C2H302)4.4H20 

Av.  interval  for  all  acetates. . 

Mg(U02).(C2H302)6.7H20.... 

K  TTOoCCoH,Oo"), 

Ca(U02)2(C2H302)6.8H20 

Mn(U02)2(C2H302)6.6H20.  .  .  . 

70.68 

From  the  list  of  general,  weighted  averages  of  the  intervals  for  the 
various  salts  (tables  97  and  98)  it  appears  that  the  frequency  interval 
of  the  single  acetates  is  larger  than  the  general  average,  corresponding 
in  this  respect  with  the  larger  interval  of  their  fluorescence  spectra,  as 
has  been  previously  noted.  The  determination  of  intervals  is,  however, 
somewhat  less  accurate  than  in  the  case  of  the  fluorescence  bands, 
and,  as  in  that  instance,  no  difference  between  various  series,  or  various 
salts,  can  be  considered  as  positively  established. 


168  FLUORESCENCE   OF  THE   URANYL   SALTS. 

Summary. 

(1)  The  spectra  of  the  uranyl  acetates  consist  of  the  usual  equi- 
distant fluorescence  bands. 

(2)  When  excitation  occurs  at  the  temperature  of  liquid  air,  these 
bands  are  resolved  into  groups  the  homologous  members  of  which  form 
series  of  constant-frequency  intervals. 

(3)  There  are  two  single  acetates — sl  finely  powdered,  anhydrous 
variety  and  a  crystalline  form  with  2  molecules  of  water  of  crystalliza- 
tion, whose  spectra  differ  widely,  particularly  as  to  the  groups  of 
fluorescence  bands. 

(4)  Of  the  double  acetates,  those  containing  lithium,  potassium, 
calcium,  manganese,  and  strontium  have  spectra  which  may  be 
regarded  as  essentially  identical  both  as  regards  the  location  of  the 
principal  bands  and  the  structure  of  the  fluorescence  groups.  The 
only  distinctions  between  their  spectra  are  in  the  sharpness  of  reso- 
lution and  relative  brightness  of  the  various  components. 

(5)  The  spectrum  of  barium  uranyl  acetate  differs  from  the  above 
in  that  the  groups  are  shifted,  as  a  whole,  about  5  frequency  units 
toward  the  red. 

(6)  In  the  spectra  of  the  double  acetates  of  ammonium  and  rubidium, 
band  D  in  each  group  is  doubled,  but  there  is  no  shift  of  the  groups. 

(7)  The  presence  of  sodium,  magnesium,  zinc,  silver,  and  lead 
modifies  the  group  structure  by  the  addition  of  bands  characteristic 
of  the  metal  and  causes  slight  relative  displacements  of  the  group 
system  as  a  whole.  Otherwise  the  spectra  resemble  those  mentioned 
under  (4). 

(8)  The  frequency  interval  for  the  fluorescence  series  of  the  double 
acetates  is  probably  the  same  for  all  series  and  for  all  salts,  the  depar- 
tures of  the  general  averages  for  the  various  salts  being  less  than  one 
frequency  unit  from  the  average  for  all,  i.  e.,  84.76.  The  same  is 
probably  true  of  the  absorption  series,  the  general  average  for  which 
is  70.68. 

(9)  The  frequency  intervals,  both  in  the  fluorescence  and  absorp- 
tion spectra,  are  larger  by  more  than  one  frequency  unit  for  the  single 
acetates  than  for  the  double  acetates. 


IX.  THE  SULPHATES. 

Uranyl  sulphate  (UO2SO4 .  3H2O)  and  the  double  uranyl  sulphates 
of  the  alkaline  metals  are  among  the  most  brilliant  of  known  fluores- 
cent substances.  Their  spectra  are  characterized  by  an  unusual  com- 
plexity of  narrow  bands  brought  out  by  cooling  to  the  temperature  of 
liquid  air.  The  group  structure  is  by  no  means  so  obviously  uniform 
as  in  the  case  of  the  compounds  already  considered,  nor  is  there  the 
marked  similarity  between  the  spectra  of  the  double  sulphates  which 
has  been  noted  in  the  discussion  of  the  fluorescence  and  absorption  of 
the  chlorides,  nitrates,  and  acetates.  There  are,  however,  certain 
characteristics  common  to  all  the  sulphates  thus  far  examined;  i.  e.: 

(1)  Fluorescence  at  —185°  vanishes  with  the  group  7  (frequency 
2000  to  2070),  which  is  the  reversing  region  for  this  family  of  salts, 
and  the  eighth  group  lies  entirely  within  the  absorption  region. 


<  1 .  1. 

II                1 

u 

il  1  .  1  . 

II       1 

NH4. 

I  ill  ill 

ill    ill 

ill 

il 

1 

il    illi 

Na 
lili        1       1     i 

1       II  1 

Na 

..ill 

II 

nil 

K 

11.11. 

liii  1  1 

K 

.     .11 

ill 

llll    1    1 

Rb 

..III 

.11  . 1 

Rb 

.III 

IN    1  1 

III        III 

II 

1 

ca 

1    1  II    II 

1 

Fig.  88. 


Fig.  89. 


(2)  Absorption  of  the  type  having  the  usual  70  =*=  frequency  interval 
extends  without  change  of  interval  into  group  7.  In  discussing  the 
acetates,  what  we  have  called  the  heads  of  the  prominent  absorption 
series  lie  in  the  region  between  2040  and  2060  instead  of  at  about 
2170,  as  in  the  spectra  of  the  acetates. 


170 


FLUORESCENCE    OF  THE    URANYL   SALTS. 


(3)  The  fluorescence  groups  are  distinguished  by  a  strong  pair  of 
bands,  fairly  dominant  in  all  the  spectra  excepting  that  of  the  sodium 
salt.  The  series  formed  by  the  members  of  shorter  wave-length  of 
these  pairs  terminates  toward  the  violet,  where  it  meets  the  head  of 
the  corresponding  absorption  series  mentioned  above. 

(4)  The  location  in  the  spectrum  of  the  fluorescence  groups  in  the 
spectrum  of  the  sulphates  is  not  approximately  the  same  for  the 
different  salts,  as  is  the  case  with  the  corresponding  double  acetates. 
On  the  contrary,  there  is  in  general  a  shift  toward  the  violet  with 
increasing  molecular  weight,  as  may  be  seen  from  figure  88,  in  which 
group  5  of  the  6  sulphates  under  consideration  are  depicted.  This 
shift  is  larger  than  that  observed  in  the  double  nitrates,  but  not 
quite  so  systematic. 

Table  99. — Uranyl  sulphate:  UOi.SOSHiO.     Fltiorescence  at  —185°  C. 

Prepared  by  extracting  an  excess  of  uranium  oxide  (UsOs)  with  sulphuric  acid  and  oxidiz- 
ing the  solution  to  UO2 .  SO4  by  means  of  H2O2.  This  neutral  solution  was  evaporated  to  crys- 
tallization. The  crystals  were  needles,  some  being  1  by  2  by  5  mm.  in  size,  apparently  ortho- 
rhombic,  with  three  good  pinacoidal  cleavages.  The  angle  of  the  optical  axes  is  very  nearly  90° 
and  the  double  refraction  is  positive. 


Group 

Group 

and 

/* 

l/nXW 

Int. 

and 

/* 

1/mX10» 

Int. 

series. 

series. 

i^ 

0.6254 

1599.0 

d. 

A 

0.5256 

1902.6 

d. 

.6223 

1606.9 

d. 

B 

.5237 

1909.5 

vd. 

B' 

.5228 

1912.7 

vd. 

B 

.6046 

1654.0 

vd. 

C 

.5210 

1919.4 

d. 

C 

.6009 

1664.2 

vd. 

C' 

.5203 

1921.9 

d. 

D 

.5976 

1673.4 

d. 

6 

D 

.5182 

1929.8 

d. 

3 

E 

.5942 

1682.9 

vd. 

E 

.5157 

1939.2 

m. 

F 

.5914 

1691.0 

d. 

F 

.5135 

1947.5 

s. 

H 

.5857 

1707.4 

vd. 

F' 

.5123 

1951.8 

m. 

[I 

.5827 

1716.1 

vd. 

H 

.5091 

1964.4 

m. 

I 

.5071 

1972.0 

d. 

B 

.5740 

1742.2 

vd. 

J 

.5054 

1978.6 

d. 

C 

.5716 

1749.4 

d. 

D 

.5686 

1758.8 

d. 

A' 

.5027 

1989.2 

d. 

E 

.5657 

1767.7 

m. 

B 

.5014 

1994.4 

vd. 

4 

F 

.3630 

1776.1 

m. 

B' 

.5004 

1998.5 

m. 

G 

.5600 

1785.7 

vd. 

C 

.4990 

2004.0 

m. 

H 

.5574 

1794.1 

d. 

cr 

.4981 

2007.6 

vd. 

I 

.5551 

1801.3 

vd. 

C" 

.4978 

2008.8 

vd. 

J 

.5534 

1807.0 

vd. 

C'" 

.4974 

2010.5 

vd. 

D 

.4964 

2014.3 

vd. 

A 

.5506 

1816.5 

d. 

7' 

D' 

.4955 

2018.2 

vd. 

B 

.5478 

1825.6 

vd. 

Et 

.4941 

2023.9 

vd. 

C 

.5450 

1834.9 

d. 

E 

.4938 

2025.3 

m. 

C 

.5441 

1837.9 

d. 

E' 

.4933 

2027.2 

d. 

D 

.5423 

1843.9 

vd. 

Fi 

.4926 

2030.0 

vd. 

5^ 

E 

.5394 

1853.8 

m. 

F 

.4917 

2033.9 

s. 

F 

.5369 

1862.4 

s. 

F' 

.4912 

2035.8 

vd. 

F' 

.5357 

1866.7 

vd. 

F" 

.4905 

2038.7 

m. 

G 

.5346 

1870.7 

vd. 

H 

.4878 

2049.9 

m. 

H 

.5321 

1879.2 

d. 

J 

.4843 

2064.8 

vd. 

I 

.5301 

1886.4 

d. 

J 

.5280 

1893.9 

vd. 

THE   SULPHATES. 


171 


If  the  above  groups  are  aligned  by  bringing  band  F  into  vertical 
registration,  as  in  figure  89,  it  will  be  seen  that  the  apparent  dissimi- 
larity in  the  composition  of  the  group  in  the  various  salts  is  due  rather 
to  the  occurrence  of  various  weak  bands  than  to  the  arrangement  of 
the  stronger  bands,  which,  while  not  identical,  approximates  to  identity 
almost  as  closely  as  in  the  acetates  or  the  nitrates.  As  in  previous 
diagrams  (see  the  chapters  dealing  with  the  spectra  of  the  chlorides, 
nitrates,  and  acetates),  the  vertical  lines  indicate  the  position  of  the 
crests  of  the  bands  and,  qualitatively  only,  their  relative  intensities. 
They  are  estimated  in  making  observations  merely  as  very  strong  (vs), 

Table  100. — Uranyl  ammonium  sulphate:  (NH 4)2.  U02.{S04)i.2H^. 
Fluorescence  at  —186°  C. 

Prepared  by  crystallizing  a  solution  of  the  two  component  salts  in  the  proportions  of  the 
double  salt.  The  composition  has  been  determined  by  Rimbach  (Ber.  d.  d.  Chem.  Ges.,  37,  479 
(1904) ;  the  crystallization  by  de  la  Provastaye  (Ann.  Chem.  Phys.  (3),  5,  51  (1842),  who  described 
it  as  being  monoclinic.  The  preparation  consisted  of  square  and  rounded  plates  of  diameter 
from  0.025  to  0.050  mm.  The  needle-like  crystals  showed  distinct  pleochroism  from  colorless 
to  yellow,  the  greatest  absorption  being  in  the  direction  of  greatest  index. 


Group 

Group 

and 

M 

1//XX103 

Int. 

and 

M 

1/mX103 

Int. 

series. 

series. 

^E 

0.6214 

1609.2 

d. 

^Hi 

0.5300 

1886.8 

vd. 

2- 

F 

.6185 

1616.7 

d. 

H 

.5295 

1888.7 

d. 

[H 

.6100 

1639.3 

d. 

5 

H' 

.5290 

1890.4 

d. 

" 

I 

.5280 

1839.3 

vd. 

B 

.6007 

1664.7 

d. 

u 

.5265 

1899.3 

vd. 

C 

.5977 

1673.1 

d. 

" 

3 

D 

.5941 

1683.2 

d. 

rA 

.5249 

1905.2 

d. 

E 

.5911 

1691.8 

s. 

Bi 

.5230 

1912.0 

vd. 

F 

.5883 

1699.7 

s. 

B 

.5214 

1917.8 

d. 

IH 

.5809 

1721.6 

vd. 

Ci 
C 

.5198 
.5194 

1923.8 
1925.4 

m. 
m. 

A 

.5755 

1737.6 

vd. 

C 

.5190 

1926.8 

m. 

B 

.5717 

1749.2 

d. 

Di 

.5177 

1931.6 

d. 

C 

.5697 

1755.3 

d. 

D 

.5169 

1934.6 

d. 

C' 

.5689 

1757.8 

d. 

6 

El 

.5152 

1941.0 

vd. 

D 

.5663 

1765.8 

m. 

E 

.5147 

1943.0 

s. 

4 

E 

.5632 

1775.5 

s. 

Fi 

.5128 

1950.1 

vd. 

F 

.5608 

1783.3 

s. 

F 

.5123 

1951.9 

vs. 

G 

.5579 

1792.3 

vd. 

F' 

.5116 

1954.7 

vd. 

Hi 

.5549 

1802.1 

vd. 

Gi 

.5106 

1958.6 

vd. 

H 

.5539 

1805.5 

m. 

H 

.5073 

1971.2 

vd. 

J 

.5508 

1815.5 

vd. 

H' 

.5066 

1974.0 

d. 

J 

.5038 

1984.9 

vd. 

fA 

.5491 

1821.2 

d. 

Bi 

.5472 

1827.5 

vd. 

fAi 

.5025 

1990.0 

d. 

B 

.5456 

1833.0 

m. 

A 

.5015 

1994.0 

vd. 

Ci 

.5440 

1838.2 

m. 

B 

.4998 

2000.9 

d. 

C 

.5435 

1840.1 

m. 

C 

.4975 

2010.0 

m. 

C' 

.5430 

1841.6 

m. 

Di 

.4960 

2016.1 

d. 

5< 

Di 

.5415 

1846.7 

vd. 

7- 

D 

.4955 

2018.3 

d. 

D 

.5406 

1849.8 

d. 

E 

.4933 

2027.1 

8. 

E 

.5380 

1858.8 

s. 

Fi 

.4916 

2034.2 

vd. 

Fi 

.5361 

1865.3 

vd. 

F 

.4912 

2036.0 

VS. 

F 

.5354 

1867.6 

s. 

F' 

.4905 

2038.7 

vd. 

F' 

.5346 

1870.6 

d. 

Gi 

.4893 

2043.7 

vd. 

Gi 

.5337 

1873.7 

vd. 

172 


FLUORESCENCE   OF   THE   URANYL   SALTS. 


strong  (s),  medium  (m),  dim  (d),  very  dim  (vd),  and  very  very  dim  (vvd) 
respectively.  No  attempt  is  made  in  the  diagram  to  indicate  the  width 
of  the  bands. 

The  spectrum  of  the  single  sulphate  resembles  those  of  the  double 
sulphates  much  more  nearly  than  is  the  case  with  the  single  and  double 
salts  of  the  other  acids. 

Wave-lengths,  frequencies,  and  relative  intensities  of  the  bands 
observed  in  the  fluorescence  spectra  of  uranyl  sulphate  and  the  double 
sulphates  of  ammonium,  sodium,  potassium,  rubidium,  and  caesium 
are  given  in  tables  99  to  104.  Similar  measurements  of  the  bands  in 
the  absorption  spectra  are  given  in  table  10.  The  determination  of 
wave-lengths  were  made  by  the  visual  and  photographic  methods  de- 
scribed in  the  foregoing  chapters. 

Table  101. — Uranyl  sodium  sulphate:  Na^.  UO2.  {SOi)2.2HtO.    Fluorescence  at  —185''  C. 

Prepared  by  crystallizing  a  solution  containing  the  two  component  salts  in  the  proportions  of 
the  double  salt.  (See  O.  de  Coninck,  Chem,  Centralblatt,  ix,  I,  919,  1905.)  The  preparation 
consisted  of  crystalline  grains  about  0.5  mm.  in  diameter,  with  much  mother  liquor  or  deliques- 
cence.    The  crystals  are  apparently  monoclinic,  with  positive  double  refraction. 


Group 

Group 

and 

M 

i/mxio^ 

Int. 

and 

M 

1/mX103 

Int. 

series. 

series. 

'B 

0.6296 

1588.3 

vd. 

D 

0.5374 

1860.8 

d. 

c 

.6255 

1598.7 

vd. 

E 

.5355 

1867.3 

d. 

2 

E 

.6182 

1617.6 

d. 

F 

.5330 

1876.0 

m. 

F 

.6151 

1625.8 

m. 

5 

G 

.5311 

1882.7 

vd. 

G 

.6122 

1633.5 

vd. 

G' 

.5301 

1886.4 

vd. 

H 

.6093 

1641.2 

vd. 

H 

.5287 

1891.4 

d. 

H' 

.5278 

1894.7 

d. 

B 

.5976 

1673.3 

d. 

I 

.5260 

1901.1 

d. 

B' 

.5963 

1677.0 

vd. 

C 

.5945 

1682.1 

d. 

A 

.5226 

1913.5 

d. 

3< 

D 

.5908 

1692.6 

d. 

B 

.5197 

1924.2 

vd. 

E 

.5880 

1700.7 

d. 

Ci 

.5181 

1930.1 

vd. 

F 

.5851 

1709.1 

s. 

C 

.5167 

1935.4 

m. 

G 

.5828 

1715.9 

d. 

Dx 

.5152 

1941.0 

d. 

H 

.5797 

1725.0 

d. 

D 

.5141 

1945.1 

vd. 

6 

E 

.5123 

1951.8 

d. 

A 

.5729 

1745.5 

vd. 

Fi 

.5110 

1956.9 

vd. 

B 

.5698 

1755.1 

m. 

F 

.5101 

1960.4 

s. 

Ci 

.5677 

1761.5 

vd. 

Gi 

.5087 

1965.8 

vd. 

C 

.5665 

1765.1 

m. 

G 

.5077 

1969.5 

vd. 

Di 

.5642 

1772.4 

d. 

Hi 

.5061 

1975.9 

d. 

D 

.5629 

1776.5 

d. 

H 

.5050 

1980.2 

m. 

4 

E 

.5607 

1784.1 

d. 

I 

.5038 

1984.9 

vd. 

F 

.5579 

1792.3 

m. 

G 

.5560 

1798.6 

vd. 

fA 

.5006 

1997.6 

vd. 

H 

.5532 

1807.7 

d. 

B: 

.4977 

2009.2 

vd. 

H' 

.5522 

1810.9 

vd. 

B 

.4965 

2013.9 

s. 

Ii 

.5509 

1815.9 

vd. 

Ci 

.4955 

2018.2 

m. 

I 

.5501 

1817.9 

vd. 

7 

c 

.4943 

2022.9 

m. 

E 

.4910 

2036.5 

m. 

A 

.5468 

1828.8 

d. 

F 

.4890 

2045.0 

d. 

B 

.5439 

1838.4 

vd. 

G 

.4873 

2052.3 

vd. 

5^ 

Ci 

.5418 

1845.7 

vd. 

H 

.4857 

2058.9 

d. 

C 

.5406 

1849.9 

m. 

H' 

.4847 

2063.1 

vd. 

Di 

.5388 

1856.0 

d. 

THE  SULPHATES. 


173 


Table  102. — Uranyl  potassium  sulphate:  Kt.UOiiSO^i.^HiO.     Fluorescence  at —185°  C. 

Prepared  by  crystallizing  a  solution  of  the  two  component  salts  in  the  proportions  of  the 
double  salt.  The  composition  has  been  determined  by  Rimbach  (Ber.  d.  d.  Chem.  Ges.,  37,  478 
(1904).  The  crystals  obtained  in  this  laboratory  were  orthorhombic.  The  preparation  con- 
sisted of  6-sided  plates  and  rounded  grains  about  0.045  mm.  in  diameter,  the  plane  of  the  optical 
axis  being  a  (100)  and  b  the  acute  bisectrix.     Double  refraction  positive. 


I 


Group 

Group 

and 

M 

1/mX10» 

Int. 

and 

M 

i/mxio» 

Int. 

series. 

» 

series. 

C 

0.6267 

1595.7 

vd. 

F' 

0.5332 

1875.5 

d. 

D 

.6229 

1605.9 

vd. 

Gi 

.5324 

1878.3 

vd. 

2- 

E 

.6188 

1616.0 

d. 

6' 

G 

.5319 

1879.9 

vd. 

F 

.6164 

1622.3 

m. 

G' 

.5314 

1881.8 

vd. 

F' 

.6150 

1625.9 

vd. 

H 

.5295 

1888.6 

vd. 

G 

.6129 

1631.6 

vd. 

I 

.5276 

1895.2 

vd. 

B 

.6010 

1663.9 

vd. 

[A' 

.5240 

1908.4 

vd. 

Ci 

.5981 

1672.0 

d. 

By 

.5235 

1910.2 

vd. 

C 

.5957 

1678.8 

d. 

B 

.5226 

1913.4 

d. 

Di 

.5941 

1683.2 

vd. 

Ci 

.5199 

1923.4 

vd. 

3 

D 

.5921 

1688.0 

vd. 

C 

.5189 

1927.2 

m. 

E 

.5886 

1698.9 

vd. 

Di 

.5173 

1933.1 

vd. 

F 

.5859 

1706.7 

m. 

D 

.5164 

1936.5 

d. 

F' 

.5851 

1709.1 

d. 

D' 

.5157 

1939.1 

vd. 

G 

.5830 

1715.3 

vd. 

6 

Ei 

.5144 

1944.0 

vd. 

H 

.5804 

1723.0 

vd. 

E 

.5137 

1946.7 

m. 

F 

.5115 

1955.4 

s. 

B 

.5718 

1748.8 

vd. 

F' 

.5107 

1958.1 

d. 

Ci 

.5697 

1755.3 

d. 

Gi 

.5097 

1961.9 

vd. 

C 

.5680 

1760.7 

d. 

G 

.5093 

1963.4 

m. 

Di 

.5662 

1766.3 

vd. 

G' 

.5088 

1965.4 

vd. 

D 

.5644 

1771.9 

d. 

H 

.5069 

1972.6 

d. 

4 

E 

.5616 

1780.5 

m. 

I 

.5054 

1978.6 

d. 

F 

.5589 

1789.1 

s. 

F' 

.5583 

1791.3 

d. 

A' 

.5023 

1991.0 

m. 

G 

.5563 

1797.5 

vd. 

Bi 

.5015 

1994.0 

vd. 

H 

.5539 

1805.5 

vd. 

B 

.5007 

1997.3 

d. 

I 

.5519 

1811.9 

vd. 

Ci 

.4988 

2004.7 

vd. 

C 

.4973 

2010.9 

s. 

A' 

.5481 

1824.5 

vd. 

Di 

.4959 

2016.5 

vd. 

B 

.5461 

1831.0 

d. 

7- 

D 

.4951 

2019.7 

m. 

Ci 

.5438 

1838.9 

d. 

El 

.4935 

2026.5 

m. 

C 

.5424 

1843.8 

m. 

E 

.4923 

2031.3 

d. 

5^ 

Di 

.5405 

1850.1 

vd. 

F 

.4906 

2038.5 

s. 

D 

.5391 

1854.9 

d. 

Gi 

.4894 

2043.3 

vd. 

El 

.5374 

1860.8 

vd. 

G 

.4889 

2045.2 

d. 

E 

.5366 

1863.5 

m. 

.G' 

.4884 

2047.5 

vd. 

F 

.5342 

1871.8 

vs. 

174 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


Table  103. — Uranyl  rubidium  sulphate:  Rh^.  UO2.  {804)3- 2H2O.    Fluorescence  at— 185°  C. 

Prepared  by  crystallizing  a  solution  containing  the  two  component  salts  in  the  proportions 
of  the  double  salt.  The  composition  has  been  determined  by  Rimbach  (Ber.  d.  d.  Chem.  Ges., 
37,  479,  1904).  The  crystallization  is  in  every  way  like  the  potassium  salt,  although  the  solubil- 
ity is  less  and  the  crystals  smaller.  The  preparation  consisted  of  6-sided  plates  about  0.02  by 
0.04  mm.  in  size. 


Group 

Group 

and 

M 

1/mX10» 

Int. 

and 

M 

1/mX10' 

Int. 

series. 

series. 

1  F 

0.6485 

1542.0 

vd. 

F' 
Gi 

0.5332 
.5320 

1875.8 
1879.7 

vd. 
vd. 

fc 

.6269 

1595.1 

d. 

5 

G 

.5310 

1883.2 

vd. 

^k 

.6225 

1606.4 

d. 

H 

.5292 

1889.5 

vd. 

.6187 

1616.4 

vd. 

J 

.5276 

1895.4 

vd. 

[F 

.6157 

1624.1 

d. 

■ 

A' 

.5240 

1908.4 

vd. 

B 

.6004 

1665.5 

vd. 

B 

.5223 

1914.5 

d. 

C 

.5975 

1673.7 

d. 

Ci 

.5198 

1923.8 

d. 

3 

C 

.5954 

1699.5 

d. 

c 

.5187 

1927.8 

m. 

D 

.5919 

1689.5 

d. 

D 

.5163 

1937.0 

d. 

E 

.5887 

1698.7 

m. 

6 

E 

.5136 

1946.9 

m. 

.F 

.5860 

1706.5 

s. 

F 

.5115 

1955.2 

vs. 

F' 

.5105 

1958.7 

vd. 

B 

.5719 

1748.5 

vd. 

Gi 

.5096 

1962.3 

vd. 

Ci 

.5692 

1757.0 

vd. 

G 

.5087 

1965.8 

vd. 

C 

.5679 

1760.9 

vd. 

H 

.5068 

1973.3 

vd. 

D 

.6643 

1772.2 

d. 

I 

.5053 

1979.0 

vd. 

4 

E 

.5616 

1780.6 

m. 

F 

.5591 

1788.7 

s. 

A' 

.5021 

1991.8 

vd. 

F' 

.5580 

1792.0 

vd. 

B 

.5008 

1996.7 

d. 

G 

.5560 

1798.6 

vd. 

Ci 

.4987 

2005.2 

d. 

H 

.5538 

1805.7 

vd. 

C 

.4973 

2010.9 

m. 

I 

.5520 

1811.6 

vd. 

7< 

D 

.4953 

2018.9 

d. 

El 

.4930 

2028.4 

d. 

B 

.5461 

1831.2 

d. 

E 

.4922 

2031.8 

d. 

Ci 

.5438 

1838.8 

d. 

F 

.4906 

2038.4 

s. 

5- 

C 

.5424 

1843.7 

d. 

G: 

.4890 

2045.1 

vd. 

D 

.5392 

1854.6 

d. 

G 

.4880 

2049.2 

vd. 

E 

.5364 

1864.3 

m. 

F 

.5342 

1871.8 

vs. 

THE  SULPHATES. 


175 


Table  104. — Uranyl  ccesium  sulphate:  Cs2U02{SOa)2  2H2O.    Fhwrescence  at  —185"  C. 

Prepared  by  precipitating  uranyl  sulphate  by  adding  caesium  sulphate  in  calculated  amount  to 
form  the  double  salt,  which  is  very  insoluble.  The  composition  of  the  crystals  is  given  as  above 
by  O.  de  Coninck  (Chem.  Centralblat,  ix,  1,  1306,  1095).  The  preparation  consisted  of  very 
small  square  plates  about  0.01  mm.  on  a  side,  the  largest  of  which  showed  an  apparently  uniaxial 
negative  figure.     The  crystals  are  therefore  presumably  tetragonal. 


Group 

Group 

and 

M 

i/mxio' 

Int. 

and 

M 

l//iX10' 

Int. 

series. 

series. 

2  F 

0.6129 

1631.8 

d. 

fEi 
E 

.5336 
0.5321 

1874.2 
1879.3 

d. 
m. 

'A 

.5989 

1669.7 

vd. 

F 

.5299 

1887.0 

s. 

B 

.5964 

1676.7 

vd. 

5- 

G 

.5276 

1895.4 

vd. 

Ci 

.59.39 

1683.8 

d. 

G' 

.5261 

1900.8 

vd. 

3 

C 

.5916 

1690.3 

d. 

H' 

.5239 

1908.6 

d. 

D 

.5894 

1696.6 

vd. 

I 

.5228 

1912.9 

vd. 

El 

.5869 

1703.9 

vd. 

E 

.5850 

1709.3 

d. 

'A 

.5189 

1927.2 

d. 

F 

.5825 

1716.6 

m. 

B 

.5168 

1935.0 

vd. 

Ci 

.5148 

1942.5 

vd. 

A 

.5695 

1755.9 

vd. 

C 

.5140 

1945.7 

m. 

B 

.5671 

1763.4 

vd. 

D 

.5118 

1953.7 

vd. 

Ci 

.5652 

1769.2 

d. 

D' 

.5110 

1956.9 

vd. 

C 

.5636 

1774.3 

d. 

6^ 

El 

.5099 

1961.0 

d. 

D 

.5612 

1782.0 

d. 

E 

.5088 

1965.5 

m. 

4 

El 

.5593 

1788.0 

d. 

F 

.5067 

1973.6 

vs. 

E 

.5574 

1794.0 

m. 

G 

.5047 

1981.4 

vd. 

F 

.5550 

1801.7 

8. 

G' 

.5035 

1986.1 

vd. 

G 

.5517 

1812.5 

vd. 

H 

.5019 

1992.6 

d. 

H 

.5490 

1821.4 

vd. 

I 

.5003 

1999.0 

m. 

I 

.5472 

1827.4 

vd. 

fA 

.4970 

2012.1 

d. 

A 

.5434 

1840.3 

d. 

C 

.4920 

2032.6 

m. 

B 

.5410 

1848.3 

vd. 

7< 

D 

.4902 

2040.0 

vd. 

5 

Ci 

.5390 

1855.2 

d. 

El 

.4888 

2045.8 

d. 

c 

.5374 

1860.8 

m. 

E 

.4874 

2051.6 

m. 

D 

.5353 

1868.0 

d. 

F 

.4858 

2058.6 

8. 

FREQUENCY  INTERVALS  OF  THE  FLUORESCENCE  SERIES. 

The  average  frequency  intervals  of  the  various  series,  as  derived 
from  the  foregoing  tables,  are  given  in  table  105,  together  with  the 
weighted  average  for  each  salt.  It  will  be  noted  that  the  intervals  of 
the  single  sulphate  and  the  double  salt  of  caesium  are  distinctly  greater 
than  the  intervals  of  the  other  four  sulphates.  There  is  nothing 
fortuitous  about  these  differences,  for,  as  will  be  seen  from  the  table, 
the  different  series  for  each  salt  have  intervals  within  one  frequency 
unit  of  the  general  average  for  that  salt,  with  three  exceptions. 

These  exceptions  are  series  Ci  in  the  ammonium  and  sodium  double 
sulphates  and  Gi  in  the  ammonium  salt.  Such  occasional  apparent 
discrepancies  are  not  uncommon  in  the  fluorescence  spectra  of  the 
uranyl  salts.  They  are  not  due  to  accidental  errors,  but  are  probably 
ascribable  to  the  complexity  of  bands  having  overlapping  components 
the  relative  intensity  of  which  in  different  portions  of  the  spectrum 
varies  progressively.  Many  such  cases  are  known.  A  doublet  ill- 
resolved  and  appearing  as  a  single  hazy  band,  the  component  of  longer 


176 


FLUORESCENCE   OF  THE   URANYL   SALTS, 


Table  105. — Average  frequency  intervals  in  the  fluorescence  spectra  of  the  sulphates. 


Series. 

Intervals. 

Weighted  averages. 

UO2SO4 
+3H2O. 

(NH4)2U02(S04)2 

+2H20. 

Na2U02(S04)3 
+2H2O. 

K2U02(S04)2 

+2H20. 

Rb2U02(S04)2 

+2H2O. 

CsjUOiCSOOs 
+2H2O. 

A 
A' 
Bi 
B 

B' 

Ci 

C 

C 

Dx 

D 

Ex 

E 

Fx 

F 

F' 

Gx 

G 

G' 

H, 

H 

H' 

I 

Jx 

J 

Average 

84.1 

84.0 

85.6 

83.3 

85.8 
"86!2" 

84.5 
83.6 

84.2 
84.2 
85.6 
84.8 

83.3 

82.8 

86.1 

85.6 
84.2 
84.6 
83.2 
83.8 

83.2 
83.1 

82.7 
83.2 

86.2 
85.6 

84.3 
84.2 

83.3 
82.8 
83.2 
82.1 

85.8 

82.5 

85.7 
85.6 

85.0 

84.6 
"85!2" 

83.6 
84.4 
83.9 
84.0 
85.0 

83.8 

83.1 

83.8 

83.3 
83.0 
82.5 

82.7 
82.9 

82.7 
83.3 

85.4 

84.4 

83.5 

86.0 
85.3 

■'85;2*" 
85.2 

84.6 
83.0 
83.6 

84.4 
84.1 
84.9 

83.2 

83.8 

85.6 

83.3 

83.7 

85.8 

84.7 

85.2 

83.7 

84.3 

83.0 

83.2 

85.7 

wave-length  being  much  stronger  in  the  bands  toward  the  red  and 
dying  away  gradually  in  subsequent  bands  as  we  approach  the  blue, 
while  the  other  component  steadily  increases,  will  give  the  effect  of  an 
increased  frequency  interval  for  the  series.  The  increase  might  easily 
be  of  the  general  order  observed  in  this  case. 

There  is  also  always  the  possibility  of  the  presence  of  a  trace  of 
another  uranyl  compound  which  would  yield  additional  series.  Such 
cases,  for  example,  are  not  uncommon  in  the  study  of  the  acetates, 
where  an  admixture  of  the  single  acetate  occurs. 

ABSORPTION  SPECTRA. 

The  difficulties  in  obtaining  a  complete  record  of  the  absorption 
bands  of  the  uranyl  sulphates  are  similar  to  those  described  in  the 
preceding  chapters.  The  transmission,  like  that  of  the  other  uranyl 
salts,  ranges  progressively  from  almost  complete  transparency  in  the 
red,  yellow,  and  green  to  a  high  degree  of  opacity  in  the  ultra-violet. 

Large,  clear  crystals  of  the  sulphates  are  not  obtainable  and  there- 
fore it  is  not  possible  to  use  very  thick  layers  and  thus  to  follow  the 
selective  absorption  far  beyond  the  reversing  region  toward  the  red, 
as  has  been  done  in  the  case  of  the  chlorides.^  The  bands  which  we 
were  able  to  locate  lie  approximately  between  2,000  and  2,600  fre- 
quency units.    They  belong  almost  exclusively  to  the  system  having 

^  H.  L.  Howes.     Physical  Review  (2),  xi,  p.  66.     1918. 


THE   SULPHATES. 


177 


the  shorter  frequency  interval  of  70=*=.  A  few  end  members  of  the 
reversing  system,  which  presumably  extends  throughout  the  fluores- 
cence region,  were  discernible.  Determinations  were  made  in  part  by 
photographing  the  spectrum  of  the  light  transmitted  by  thin  layers, 
in  part  by  the  method  of  reflection. 

In  table  106  the  frequencies  of  the  bands  in  the  spectra  of  the  6 
sulphates  are  arranged  by  series.  Each  series,  as  usual,  is  designated 
by  a  small  letter  corresponding  to  the  capital  letter  which  denotes  the 
fluorescence  series  to  which  it  is  related. 

Table  106. — Absorption  spectra  of  uranyl  sulphates  at  —180°  C. 


Salt. 

Series. 

Frequencies. 

Average 
interval. 

ai 

2056.8        2128.1         2399.8 

68.6 

a 

2060.6         2202.2         

70.8 

b' 

2068.7         2140.5         2209.2 



70.1 

dx 

2218.3          

d 

2016.1         2081.2        2152.9 

68.4 

UO2SO4+3H2O. 

A 

e 

2093.6        2160.3         2229.5 

68.0 

fi 

2029.9         2170             

70.1 

f 

2102.6        2236.9        2373.0 

70.1 

r 

2035.8        2102.6         

hi 

2045.8        2115.9         2186.7 

2327.2         

70.3 

[f^ 

2260.4         

General  average 



69.6 

2061.2        2135.3         2205.8 

2276.3         

a 

71.3 

b 

2072.5         2212.4         

69.9 

c 

2082.8         2155.1         2226.2 

2295.2         2510.0 

71.2 

di 

2016.5  (R)2199.8        2263.0 

2409.6         

69.9 

e 

2096.0         2236.2         2305.7 

2444.4         

69.6 

(NH4)2U02(S04), 

+2H20. 

e' 
/i 

2031.8         2448.6         

2244.4         2315.6         2383.3 

2524.6        2595! 4 

69.6 
70.2 

/ 

2107.7        2178.7        2250.0 

2454.3         

69.3 

/' 

2039.6         2253.8        2323.8 

2392.0        2464.0 
2532.8 

70.4 

(71 

2044.0        2116.0        2187.1 

71.5 

0 

2330.5         2401.0        2541.0 

70.2 

h 

2127.7        2198.8        2236.0 

2409.6        2477.1 

70.3 

General  average 

2549.4 

70.3 

2069.5         

fo 

a' 

2144.5        2214.7         



70.2 

b 

2080.8         2153.3          



72.5 

c 

2093.7        2306.8        2375.9 

70.5 

dx 

2167.3         

d 

2172.5        2243.8        2314.8 

2385.6         

71.0 

Na,UOj(S04)2 
+2H2O. 

e 

2035.8  2107.5        2250.1 
2039.2          

2043.9  2114.3         2184.5 



71.4 
'76!3'" 

Qx 

2050.0        2120.3         2260.4 



70.1 

0 

2190.1          





Q' 

2054.7         

2055.2          





h 

2063.4        2128.6        2199.9 

71.3 

.h' 

2135.2        2207.7         

General  average 



72.1 

71.3 

178  FLUORESCENCE   OF  THE   URANYL   SALTS. 

Table  106. — Absorption  spectra  of  uranyl  sulphates  at  —180°  C — continued. 


Salt. 

Series. 

Frequencies. 

Average 
interval. 

f6i 

2063.1         2412.3 

69.8 

b 

2064.4         2136.4 

2204.6 

2276.9 

70.8 

b' 

2065.7         2341.0 

68.8 

Cl 

2071.9         2353.5 



70.4 

c 

2078.6         2289.4 

70.2 

di 

2017.3         2444.1 

71.1 

d 

2375.3          

d' 

2158.2         

K2U02(S04)2 

ei 

2174.0         



+2H,0. 

e 

2095.5         2307.0 

2379.8 

7i.i 

e' 

2241.7         2312.1 

2385.0 

71.6 

/i 

2035.0         2106.8 

2246.7 

70.6 

/ 

2039.6         2109.3 

2179.4 

2248.2 

2390.6 

70.2 

/' 

2250.7         



<7i 

2293.5         

0 

2116.4         2188.5 

2256.7 

2323.7 

69.1 

a' 

2047.9         







[h 

2056.8        2266.3 

General  aver 
2065.6         2136.6 

age 

69.8 

70.3 

2205.7 

2275.1 

[bi 

69.8 

b 

2071.2         



Cl 

2218.8         

c 

2434.3         

dx 

2014.9         

d 

2230.2         2301.0 

2443.2 

71.0 

d' 

2370.5         

Rb2U02(S04)2 

+2H2O. 

• 

ei 
e 
e' 

2028.4         2096.2 
2241.2         2307.3 
2312.2         

2375.1 
2378.7 

2449.8 



70.2 
68.8 

h 

2106.6         2174.5 

2249.2 

71.3 

f 

2037.9         2107.6 

69.7 

r 

2040.3         2109.7 

2179.4 

2385.7 

69.1 

Oi 

2045.4         2322.0 

2391.3 

69.2 

0 

2048.5         2117.7 

2187.7 

2256.7 

2325.8 

69.3 

hi 

2193.9          

[h 

2085.5         2267.3 

General  aver 
2096.0        2165.4 

2340.8 
age 

2408.5 

70.0 

69.8 

2236.9 

2375.9 

2445.0 

^a 

70.3 

2517.7 

a' 

2311.9         

c 

2103.5         



c' 

2035.8         2106.4 

70.6 

dx 

2115.1          

CS2U02(S04)2 
4-2H2O. 

e 

2120.0         2261.0 

2329.6 

2399.8 
2542.8 

2471.0 
2613.4 

70.5 

/ 

2061.2         2130.8 

2266.6 



69.7 

/' 

2133.4          

Q 

2065.5         2206.5 

2279.5 

71.3 

Q' 

2071.9         2143.6 

2215.8 

2353.1 
2498.3 

2426.9 
2567.2 

70.8 

h 

2077.2          

^% 

2084.6         2294.1 
General  aver 

age 

69.8 

70.4 

THE  SULPHATES. 


179 


Table  107. — Average  frequency  intervals  for  the  six  sulphates. 


UO2SO4 69.6 

(NH4)2U02(S04)2 70.3 

Na2U02(S04)2 71.3 


K2U02(S04)2 70.3 

RB2U02(S04)2 69.8 

Cs2U02(S04)2 70.4 


As  is  frequently  the  case  in  these  absorption  spectra,  one  or  more 
bands  of  a  given  series  are  commonly  missing  or  at  least  not  discerni- 
ble in  the  negatives.  On  the  other  hand,  nearly  all  the  bands  are 
found  to  be  members  of  a  series  which  is  definitely  related  to  a  fluores- 
cence series  and  has  the  proper  frequency  interval.  The  occasional 
isolated  bands,  moreover,  are  so  located  that  they  may  be  definitely 
associated  with  a  fluorescence  series  and  may  reasonably  be  classed  as  the 
sole  visible  member  of  an  absorption  series  the  remainder  of  which 
fails  to  appear  in  our  photographs. 

These  show  no  systematic  departure  from  the  general  average  (70.3) 
for  the  entire  group.  Lying  as  they  do  within  one  frequency  unit  of 
the  average,  we  may  fairly  conclude  that  within  the  errors  of  observa- 
tion, which  are  rather  large  on  account  of  the  lack  of  definition  and 
incomplete  resolution  of  these  absorption  groups,  the  various  sulphates 
have  a  common  frequency  interval. 

The  frequency  intervals  of  the  various  series  of  a  given  salt  depart 
somewhat  more  widely  from  the  average  for  that  salt,  but  again  there 
is  no  systematic  variation,  and  it  is  probable  that  all  the  series  would 
be  found  to  have  the  same  interval,  were  it  possible  to  locate  the  bands 
with  greater  certainty. 

Summary. 

(1)  The  fluorescence  spectrum  of  the  uranyl  sulphates  consists  of 
8  equidistant  bands,  the  first  and  eighth  of  which  disappear  at  the 
temperature  of  liquid  air. 

(2)  The  remaining  bands  are  resolved  into  groups  of  narrow  line- 
like bands,  the  homologous  members  of  which  form  series  having 
constant  frequency  intervals,  ranging  from  85.7  in  caesium  uranyl 
sulphate  to  83.0  in  potassium  uranyl  sulphate. 

(3)  The  fluorescence  groups  are  distinguished  by  a  strong  pair  of 
bands  about  8  frequency  units  apart  and  7  weak  bands,  some  of  which 
are  doublets. 

(4)  There  is  a  shift  of  all  bands  toward  the  violet,  with  increasing 
molecular  weights,  of  about  15  frequency  units  in  passing  from  the 
spectrum  of  uranyl  sulphate  to  that  of  caesium  uranyl  sulphate. 

(5)  The  absorption  spectra  of  the  sulphates  are  made  up  of  series  of 
bands  having  a  frequency  interval  of  70.3  (general  average). 

(6)  These  absorption  series  extend  into  group  7  of  the  fluorescence 
without  break  of  interval.  There  are  many  reversals  where  fluorescence 
and  absorption  overlap.  The  reversing  region  is  therefore  one  group 
farther  toward  the  red  than  in  most  spectra  of  the  uranyl  compounds. 


X.  THE  FLUORESCENCE  OF  FROZEN  SOLUTIONS. 

The  fluorescence  spectra  of  solutions  generally  consist  of  only  one 
or  two  very  broad  bands.  Such  bands  undoubtedly  possess  component 
bands  in  considerable  number,  but  spectrum  analysis  often  fails  to 
reveal  them  because  of  extensive  overlapping.  Chlorophyl  in  alcohol 
possesses  a  series  of  absorption  bands^  which  resemble  the  absorption 
bands  of  the  uranyl  solutions.  The  very  broad  fluorescence  band  in 
the  orange  and  red  probably  consists  of  several  components  which 
form  a  similar  series.  Anthracene  in  solution^  presents  a  fluorescence 
series  of  at  least  4  bands  which  strongly  resembles  the  series  found  in 
the  fluorescence  spectra  of  uranyl  solutions. 

Probably  the  first  observer  to  note  the  fact  that  uranyl  solutions 
yield  fluorescence  spectra  consisting  of  several  bands  was  G.  C.  Stokes.^ 
He  states  that  ''a  solution  of  nitrate  of  uranium  is  decidedly  sensi- 
tive," i.  e.j  fluorescent.  Later,  in  the  same  paper,  he  writes  ''I  have 
observed  seven  of  these  bands  arranged  at  regular  intervals."  E. 
Becquerel,*  in  his  monumental  work  on  the  uranyl  salts,  makes  this 
observation : 

"  Certain  solutions  of  the  salts  of  uranium  give,  in  the  violet  rays,  a  luminous 
emission  scarcely  less  brilliant  than  the  crystals  themselves  ....  several 
[bands]  appear  to  correspond  to  the  bands  given  by  the  solid  salts;  the  sul- 
phate and  the  double  sulphate  of  potassium  and  uranium  are  in  this  class." 

In  the  same  year  Hagenbach,^  who  was  studying  many  fluorescence 
materials,  observed  that  the  uranyl  oxide  in  nitric  acid  shows  8  very 
sharply  outlined  maxima  in  the  fluorescence  spectrum.  Morton  and 
Bolton®  studied  the  absorption  of  the  uranyl  solutions  and  noted  the 
fluorescence.  These  investigators  were  the  first  to  recognize  the 
possibility  of  the  existence  of  more  than  one  hydrate  of  the  same  salt, 
which,  they  state,  *^  enables  us  to  explain  some  discrepancies  of  authori- 
ties on  this  point."  Our  present  work  has  brought  out  the  necessity, 
of  such  a  hypothesis.  Jones  and  Strong,^  following  the  same  method 
as  Morton  and  Bolton,  have  published  the  most  extensive  data  on  the 
absorption  spectra,  but  their  work  does  not  include  temperatures 
below  the  freezing-point. 

This  chapter  contains  the  results  of  experiments  which  were  de- 
scribed in  two  papers,  together  with  some  additional  data  heretofore 
unpublished.    The  first,  a  preliminary  paper,  ^  showed  that  the  bands  of 

^  Nichols  and  Merritt.     Carnegie  Inst.  Wash.  Pub.  No.  130,  p.  85.     1910. 
'Louise  MacDowell.     Physical  Review  (1),  26,  p.  155.     1908. 
'  Stokes.     Philosophical  Transactions,  p.  463.     1852. 

*  E.  Becquerel.     Comptes  Rendus,  75,  p.  296.     1872. 

5  Hagenbach.     Poggendorf  Annalen,  146,  p.  582.     1872. 

«  Morton  and  Bolton.     Chemical  News,  pp.  113,  164.     1873. 

'  Carnegie  Inst.  Wash.  Pub.  No.  130. 

*  Nichols  and  Merritt.     Physical  Review  (2),  3,  p.  457.     1914. 

180 


FROZEN   SOLUTIONS. 


181 


the  solutions,  even  at  — 180°,  resembled  in  breadth  and  regular  spacing 
those  of  the  solid  salts  at  room  temperature.  The  uranyl  acetate  in 
alcohol  proved  to  be  the  exception,  since  at  —180°  it  resolved  into 
faint  lines,  which  did  not,  however,  coincide  in  position  with  those  of 
the  solid  acetate  at  that  temperature. 

The  variety  of  shifts  with  systematic  dilution  and  temperature 
change  led  to  the  second  investigation,^  in  the  hope  that  some  general 
law  of  shift  might  be  deduced.  It  was  also  planned  to  study  the  funda- 
mental relations  between  concentration  and  frequency  interval, 
temperature,  and  state  of  resolution,  etc.  With  these  relations  in  view 
much  work  was  done  which  led  to  the  discovery  of  many  beautiful 
and  unique  spectra. 

EXPERIMENTAL  METHOD. 

For  the  study  of  the  spectra,  except  where  otherwise  specified,  a 
Hilger  constant-deviation  spectrometer  was  used. 

The  apparatus  for  the  cool- 
ing and  excitation  of  the  sub- 
stances under  observation 
was  designed  to  enable  the 
observer  to  hold  the  tempera- 
ture of  the  specimen  con- 
stant at  any  temperature 
between  0°  and  -180°  C. 
The  mounting  consisted  of  a 
cylindrical  copper  block  M 
(fig.  90),  the  top  of  which 
was  bored  to  receive  a  small 
test-tube  F,  which  contained 
the  fluorescent  solution.  The 
side  of  the  block  was 
channeled  to  let  the  exciting 
light  fall  on  the  specimen  and 
to  let  the  fluorescent  light 
out.  To  the  bottom  of  this 
copper  block  was  soldered  a 
cylinder  of  sheet  copper, 
which  could  be  partially  or 
completely  covered  by  the 
liquid  air  in  the  unsilvered 
Dewar  bulb  D,  thus  produc- 
ing different  temperatures  in 
the  specimen.  This  mount- 
ing was  rigidly  suspended 
from  above  by  partially  non- 


FiG.  90. 


Howes.     Physical  Review  (2),  vol.  6,  p.  193.     1915. 


182  FLUORESCENCE    OF  THE   URANYL   SALTS. 

conducting  material .  The  Dewar  bulb  was  fastened  to  an  adjustable 
support  Hj  and  the  mounting  could  be  submerged  in  the  liquid  air 
to  various  depths  by  raising  or  lowering  the  bulb  by  means  of  a  cord  R. 

Fluorescence  was  excited  by  the  rays  from  a  carbon  arc  A.  The 
light  passed  successively  through  a  water-cell  W,  a  large  short-focused 
condenser  C,  and  a  solution  of  ammonio-copper  sulphate  B.  This 
solution  absorbed  all  of  the  exciting  light  of  a  wave-length  greater 
than  0.4780  ix,  so  that  the  fluorescent  light,  which  entered  the  colli- 
mator slit  S  of  the  spectrometer,  could  be  viewed  on  a  black  back- 
ground. A  small  resistance  coil  T  was  inserted  in  a  glass  tube,  which 
was  always  placed  in  the  middle  of  the  solution.  The  temperatures 
were  recorded  on  a  Callender  recorder.  The  massive  copper  block  M 
served  to  reduce  the  vertical  temperature  gradient  in  the  frozen  solu- 
tion to  less  than  1°  per  centimeter.  It  made  the  apparatus  rather  slow 
in  responding  to  changes,  but  afforded  an  excellent  control  of  tempera- 
ture. 

The  salts  were  carefully  weighed  and  *' normal'^  solutions  were 
prepared.^  Acid  solutions  were  made  by  adding  a  definite  volume  of 
the  commercial  concentrated  acid  to  a  definite  volume  of  a  water 
solution  of  known  concentration. 

Although  readings  were  taken  and  tables  made  in  units  of  wave- 
length, the  diagrams  of  spectra  are  plotted  on  an  arbitrary  scale  of 
frequencies,  ^.  e.,  l/ix  X  10^ 

URANYL  SULPHATE  IN  AQUEOUS  SOLUTION. 

The  uranyl  sulphate  in  water,  upon  excitation  with  the  carbon  arc, 
yields  4  bands  at  +20°  C;  but  when  cooled  6  bands  are  visible,  the 
new  bands  being  of  longer  wave-lengths.  This  phenomenon — increase 
of  intensity  with  cooling — is  a  very  fortunate  one,  for  otherwise  the 
study  of  the  more  dilute  solutions  would  be  limited  to  the  lowest 
temperatures.  In  table  108  will  be  found  the  bands  of  the  1/1,  1/10, 
1/100,  and  1/1000  normal  aqueous  solutions.  In  the  spectrum  of  the 
1/1  normal  solution  band  7  is  at  0.4927  ix  at  +20°,  which  is  of  interest 
because  the  crystalline  salt  was  found  to  give  a  fluorescence  band  at 
0.4925.2 

If  a  reasonable  error  is  assumed,  these  bands  may  be  considered  to 
be  coincident.  In  this  region  they  are  approximately  75  a.u.  in  width; 
hence  measurements  were  taken  on  the  crest  rather  than  on  the  middle 
of  the  band,  the  crests  being  located  slightly  nearer  the  violet  edge. 

The  absorption  spectrum^  of  the  normal  solution  presents  a  band  in 
this  region  at  0.4910,  which  is  17  A.u.  nearer  the  violet  than  the  fluores- 

^  The  term  "normal"  solution,  as  used  in  this  paper,  means  one  which  contains  the  same  num- 
ber of  grams  of  solute  to  the  liter  of  solvent  as  the  nvmaber  which  represents  the  molecular  weight 
of  the  particular  salt  dissolved. 

2  Nichols  and  Merritt.     Physical  Review  (1),  33,  p.  354.     1911. 

'  Jones  and  Strong.     Carnegie  Inst.  Wash.  Pub.  No.  130,  p.  109. 


FROZEN   SOLUTIONS. 


183 


cence  band.  Jones  and  Strong  employed  the  continuous  spectrum  of 
the  Nernst  lamp,  which  produces  fluorescence  in  this  region.  Such 
luminescence,  although  masked  by  the  more  intense  background, 
tends  to  shift  the  crest  of  the  absorption  band  toward  the  violet. 

A  comparison  of  the  wave-lengths  of  the  bands  of  the  solid  with 
those  of  the  solution  indicates  a  progressive  difference.  When  the 
spectra  of  the  solution  and  of  the  soHd  are  plotted  in  frequency  units, 
either  is  found  to  include  only  one  series  of  bands,  those  of  the  solution 
being  of  a  slightly  smaller  interval  than  those  of  the  solid. 

Table  108. — Uranyl  sulphate  in  water. ^ 


Solution  and  temp. 

Band  2. 

Band  3. 

Band  4. 

Band  6. 

Band  6. 

Band  7. 

Normal 
solution, 

1/10 
normal 
solution. 

1/100 
normal 
solution. 

1/1000 
normal 
solution. 

[+  20 
0 

-  35 

-  60 

-  90 
-120 
-150 
-180 

■+  20 

-  30 

-  60 

-  90 
-120 
-150 

^-180 

-  35 

-  60 

-  90 
-120 
-150 
-180 

'-  90 
-120 
-150 

0.5641 
.5641 
.5641 
.5637 
.5635 
.5634 
.5634 
.5636 

.5636 
.5631 
.5629 
.5621 
.5624 
.5629 
.5633 

.5633 
.5634 
.5631 
.5629 
.5631 
.5638 

.5583 
.5574 
.5574 

0.5383 
.5383 
.5378 
.5376 
.5370 
.5370 
.5373 
.5375 

.5379 
.5373 
.5368 
.5364 
.5365 
.5367 
.5371 

.5373 
.5373 
.5368 
.5365 
.5368 
.5370 

.5330 
.5324 
.5345 

0.5143 
.5141 
.5141 
.5137 
.5131 
.5133 
.5136 
.5140 

.5139 
.5136 
.5130 
.5125 
.5127 
.5130 
.5133 

.5135 
.5129 
.5125 
.5126 
.6129 
.5132 

.5102 
.5097 
.5105 

0.4927 
.4926 
.4927 
.4924 
.4919 
.4919 
.4919 
.4921 

.4918 
.4913 
.4911 
.4910 
.4909 
.4913 
.4916 

.4913 
.4911 
.4907 
.4907 
.4909 
.4911 

.4904 
.4904 
.4909 

6! 6229* 
.6227 
.6230 
.6235 
.6241 

0.5934 
.5928 
.5923 
.5923 
.5924 
.5924 



".'6228" 
.6231 

.5911 
.5904 
.5904 
.5917 
.5921 



.5924 
.5928 

*  The  numbers  by  which  unresolved  bands  are  designated  in  this  and  the  following  tables 
correspond  to  the  group  numbers  used  in  previous  chapters,  since  each  band  corresponds  to  a 
group  in  the  resolved  spectra  of  the  crystallized  salts. 

In  figure  91,  band  5  is  seen  to  shift  with  falHng  temperature  toward 
the  violet,  the  shift  amounting  to  13  A.u.  when  a  temperature  of 
— 100°  is  reached.  With  further  cooling  to  — 180°  the  band  shifts  back 
toward  the  red.  It  would  be  interesting  to  ascertain  whether  this  shift 
toward  the  red  would  continue  with  further  decrease  in  temperature. 
The  other  bands  of  the  normal  solution  behave  similarly  with  falling 
temperature,  i.  e.,  the  entire  spectrum  undergoes  a  shift  to  the  violet, 
followed  by  a  reverse  shift  to  the  red.  The  wave-lengths  of  the  bands 
at  —180°  are  approximately  the  same  as  the  wave-lengths  at  —60°. 


184 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Jones  and  Strong  discovered  a  shift  of  15  A.u.  toward  the  red  for 
the  absorption  band  of  wave-length  0.4910  when  the  temperature  of 
their  solution  was  raised  from  +5°  to  +84^.  Our  fluorescence  band 
at  0.4927  shifts  in  the  same  direction,  with  a  rise  in  temperature  from 
-90°  to  +20°. 

H.  Becquerel  beUeved  that  any  modification  of  the  absorption 
spectrum  is  accompanied  by  a  similar  change  in  the  fluorescence  spec- 
trum, and  these  shifts  lend  strength  to  his  generalization. 

A  brief  study  of  the  fluorescence  spectra  of  the  1/10  and  the  1/100 
normal  solutions  at  different  temperatures  indicates  that  a  similar 
temperature  shift  occurs. 


-120 


-lecP. 


Fig.  91. — Uranyl  sulphate — Temperature  shift. 

(1)  1/1  normal,   aqueous:   (2)  1/10  normal,  aqueous:  (3)  1/100  normal,  aqueous;   (4)  40  c.o.  1/10  normal, 
aqueous  to  1  c.c.  sulphuric  acid;   (5)  1  c.c.  1/10  normal,  aqueous  to  1  c.c.  sulphuric  acid. 

The  increase  in  the  amount  of  solvent  produces  a  shift  of  the  spec- 
trum toward  the  violet.  For  example,  band  7  at  —90°  shifts  as  fol- 
lows: in  the  1/1  normal  solution  the  wave-length  is  0.4919,  in  the  1/10 
normal  0.4910,  in  the  1/100  normal  0.4907,  in  the  1/1000  normal 
0.4904  fjL. 

The  1/1000  normal  solution  shows  a  spectrum  which  is  very  strongly 
shifted  toward  the  violet  The  above  comparison  of  the  wave-lengths 
of  band  7  fails  to  indicate  the  shift  of  the  spectrum,  because  it  is  accom- 
panied by  a  marked  decrease  in  interval,  while  of  all  the  bands,  number 
7  is  the  least  shifted.  For  example,  band  4  of  the  1/1000  normal  at  a 
temperature  of  —90°  is  of  wave-length  0.5583,  while  band  4  of  the 
1/100  normal  at  -90°  is  of  wave-length  0.5631  units.  Bands  5,  6,  and 
7  show  progressively  less  variance  in  wave-length  with  the  correspond- 
ing bands  of  the  1/100  normal  solution  because  of  the  shorter  frequency 
of  the  1/1000  normal  interval.  Measurements  of  these  spectra  plotted 
on  a  frequency  scale  indicate  that  while  the  bands  are  spaced  by  about 
85.7  units  in  the  1/1,  1/10,  and  1/100  normal  solutions,  the  1/1000 


FROZEN   SOLUTIONS. 


185 


normal  bands  are  of  only  82  units  interval.    (See  table  109.)    This  may 
be  due  to  a  change  in  the  ionization  with  dilution. 

To  ascertain  whether  the  rate  of  cooling  caused  a  change  in  the 
spectra,  a  solution  was  suddenly  plunged  into  liquid  air  and  excited  to 
fluorescence.  Measurements  were  then  taken  on  the  bands,  but  no 
change  in  wave-lengths  was  observed. 

Table  109. — Uranyl  sulphate  in  water.   Frequencies  and  average  intervals  of  fluorescence  bands. 


Band. 

+20° 

0« 

-35° 

-60° 

-90° 

-120° 

-150° 

-180° 

Frequencies 
in  normal 
solution. 

'2 
3 

4 
5 
6 

7 

1605.4 
1686.9 
1773.9 
1860.1 
1946.7 
2030.9 

1605.9 
1688.3 
1774.6 
1862.2 
1948.9 
2032.9 

1605.1 
1688.3 
1774.9 
1862.2 
1948.2 
2032.9 

1603 . 8 
1688.0 
1774.9 
1861.2 
1947.0 
2032.1 

1602.3 
1688.0 
1774.3 
1860.5 
1945.5 
2030.0 

1685.2 
1772.7 
1857.7 
1945 . 1 
2029.6 

1772.7 
1857.7 
1944.4 
2029.5 

1772.7 

1857.7 
1945.1 
20.30.0 

Average  int . . 

85.6 

85.8 

86.1 

85.1 

85.4 

85.6 

85.7 

85.5 

Frequencies 
in  1/10 
normal 
solution. 

2 
3 
4 
5 
6 
7 

1605.6 
1690.0 
1776.5 
1863.3 
1949.3 
2035.4 

1604.9 
1688.9 
1775.8 
1861.9 
1948.2 
2034.2 

1691.8 
1776.5 
1862.9 
1949.3 
2036.2 

1693.8 
1779.0 
1864.3 
1951.2 
2036.7 

1693.8 
1778.1 
1863.9 
1950.5 
2037.1 

1774.3 
1859.1 
1945.9 
2033.3 

;;;;;;;; 

1775.9 
1861.2 
1947.0 
2035.4 

Average  int .  . 

86.3 

86.5 

86.1 

85.7 

85.8 

86.0 

85.9 

Frequencies 
in  1/100 
,  normal 
solution. 

3 

4 
5 
6 

7 

1688.0 
1775.9 
1862.9 
1949.7 
2037.1 

1686.9 
1773.7 
1862.3 
1948.6 
2036.2 

1775.3 
1861.2 
1947.4 
2035.4 

1774.9 
1861.2 
1949.7 
2036.2 

1775.9 
1862.9 
1951.2 
2037.9 

1776.5 
1863.9 
1950.8 
2037.9 

Average  int 

86.7 

87.1 

87.3 

87.1 

87.3 

87.3 

Frequencies   (4 

in  1/1000     15 

normal        1 6 

solution.      [7 

1791.2 
1876.2 
1960.0 
2039.4 

1794.0 
1878.3 
1961.9 
2039.4 

1794.0 
1870.9 
1958.9 
2037.1 

1794.0 
1870.9 
1958.9 

Average  inl 

82.7 

81.8 

81.0 

82.4 

URANYL  SULPHATE  MIXED  WITH  SULPHURIC  ACID. 

It  has  been  observed  that  the  bands  of  the  aqueous  solutions  move 
toward  the  violet  with  progressive  dilution  with  water;  hence  it  was 
of  considerable  interest  to  ascertain  the  effect  of  dilution  with  sul- 
phuric acid. 

The  addition  of  one  volume  of  acid  to  40  volumes  of  the  1/10  normal 
aqueous  solution  (table  110)  produces  a  negligible  effect,  but  a  mixture 
of  equal  volumes  shifts  the  bands  back  toward  the  red,  in  fact,  the 
wave-lengths  of  the  bands  at  +20°  are  longer  than  those  of  the  normal 
solution — aqueous.  This  can  be  discovered  from  a  comparison  of  the 
wave-lengths  of  the  1/10  normal  solutions  with  those  of  the  normal 
solutions  in  tables  108  and  110.    The  effect  is  not  evident  at  low  tern- 


186 


FLUORESCENCE    OF   THE    URANYL    SALTS. 


peratures,  because  the  spectrum  of  the  1  to  1  acid  solution  persistently 
shifts  toward  the  red  instead  of  reverse  shifting  at  —100"^  (see  fig.  91). 
The  frequency  interval  remains  unchanged,  with  a  proportionately 
large  acid  dilution. 

Table  110. — Uranyl  sulphate  in  sulphuric  acid. 


Temp.,  etc. 

Band  2. 

Band  3. 

Band  4. 

Band  5. 

Band  6. 

Band  7. 

'+  10° 
-  30° 

0.5634 
.5635 

0.5376 
.5376 

0.5140 
.5139 

0.4931 
.4928 

0.5929 

40  c.c.  of  0.1  normal  aque- 

- 60° 

0.6238 

.5924 

.5631 

.5.373 

.5135 

.4919 

ous  solution  with  1  c.c. 

-  90° 

.6224 

.5910 

5621 

.5365 

.5129 

.4919 

of  acid. 

-120° 

.6226 

.5914 

.5625 

.5362 

.5126 

.4920 

-150° 

.6234 

.5918 

.5627 

.5365 

.5128 

.4925 

[-180° 

.6242 

.5919 

.5630 

.5367 

.5130 

.4925 

f-l-  20° 

.5945 

.5657 

.5388 

.5149 

.4921 

-  30° 

.6246 

.5935 

.5640 

.5376 

.5139 

.4916 

1  c.c.  of  0.1  normal  aque- 

- 60° 

.6231 

.5921 

.5630 

.5368 

.5133 

.4911 

ous  solution  with  1  c.c- 

-  90° 

.6215 

.5906 

.5616 

.5359 

.5124 

.4905 

of  acid. 

-120° 

.6199 

.5893 

.5608 

.5348 

.5114 

.4898 

-150° 

.6203 

.5893 

.5607 

.5347 

.5113 

.4897 

[-172° 

.6203 

.5890 

.5602 

.5345 

.5109 

.4893 

Table  111.— Uranyl 

su 

Iphate  in  sulphuric  acid. — Frequencies  and  average  intervals  of 
fluorescence  bands. 

Band. 

4-10° 

-30° 

-60° 

-90° 

-120° 

-150° 

-180° 

Frequencies  of  40  c.c.  of 
0.1  normal  aqueous' 
with  1.0  c.c.  of  acid. 

2 
3 

4 
5 
6 

7 

1603.1 
1688.0 
1775.9 
1861.2 
1947.4 
2032.9 

1606.7 
1692.0 
1779.0 
1863.9 
1949.7 
2032.9 

1606.2 
1690.9 
1777.8 
1865.0 
1950.8 
2032.5 

1604.1 
1689.8 
1777.1 
1863.9 
1950.1 
2030.5 

1602.1 
1689.5 
1776.1 
1863.2 
1949.3 
2030.5 

1860.1 
1945.5 
2028.0 

1686.7 
1774.6 
1860.1 
1945.9 
2029.2 

Average  interval. . . 

84.4 

85.6 

86.0 

85.2 

85.3 

85.3 

85.7 

Frequencies  of  1  c.c.  of 
0.1  normal  aqueous' 
with  1  c.c.  of  acid. 

2 
3 
4 
5 
6 
7 

1682!!' 

1767.7 

1856.0 

1942.1 

2032.1 

1601.0 
1684.9 
1773.1 
1860.0 
1945.9 
2034.2 

1604.9 
1688.9 
1776.2 
1862.9 
1948.2 
2036.2 

1609.0 
1693.4 
1780.6 
1866.0 
1951.6 
2038.7 

1613.2 
1696.9 
1783.2 
1869.9 
1955.4 
2041.7 

1612.1 
1696.9 
1783.5 
1870.2 
1955.8 
2042.1 

1612.1 
1697.8 
1785.1 
1870.9 
1957.3 
2043.7 

Average  interval 

... 

87.5 

86.6 

86.3 

86.0 

85.7 

86.0 

86.3 

URANYL  POTASSIUM  SULPHATE  IN  WATER. 

The  spectra  of  the  aqueous  solutions  of  uranyl  potassium  sulphate, 
like  those  of  uranyl  sulphate,  consist  of  a  single  series  of  bands. 

The  temperature  shift  of  the  more  concentrated  solutions,  e.  g,,  the 
1/15  and  1/150  normal,  is  at  first  toward  the  violet,  followed  by  a 
reverse  shift  toward  the  red.  The  wave-lengths  of  the  bands  of  the 
aqueous  solutions  are  recorded  in  table  112.  It  will  be  seen  that  the 
shift  toward  the  red  is  more  marked  than  in  the  uranyl  sulphate  solu- 
tions.   (See  also  fig.  92.) 


FROZEN   SOLUTIONS. 


187 


The  1/1500  and  1/15,000  normal  solutions  yield  bands  which  present 
a  hazy  appearance,  lacking  the  pronounced  crests  of  the  more  con- 
centrated solutions.  For  this  reason  the  readings  of  such  wave- 
lengths are  more  likely  to  be  in  error.  The  same  tendency  to  first 
shift  toward  the  violet  and  then  shift  toward  the  red  is  evident. 

Table  112. — Uranyl  potassium  sulphate  in  water. 


Solution  and  temp. 

Band  3. 

Band  4. 

Band  5. 

Band  6. 

Band  7. 

f+  20° 

0.5656 

0.5388 

0.5154 

0.4932 

0° 

.5651 

.5387 

.5152 

.4928 

1/15 

-  30° 

0.5942 

.5650 

.5386 

.5148 

.4926 

normal 

-  60° 

.5945 

.5652 

.5386 

.5148 

.4927 

solution. 

-  90° 

.5945 

.5653 

.5386 

.5148 

.4925 

-120° 

.5946 

.5653 

.5387 

.5149 

.4928 

-150° 

.5953 

.5653 

.5393 

.5154 

.4933 

[-180° 

.5966 

.5669 

.5406 

.5166 

.4945 

f+  20° 

.5398 

.5155 

-  30° 

.5659 

.5391 

.5153 

.4931 

1/150 

-  60° 

.5657 

.5388 

.5152 

.4928 

normal    -J 

-  90° 

.5657 

.5393 

.5153 

.4931 

solution. 

-120° 

.5656 

.5394 

.5152 

.4932 

-150° 

.5956 

.5667 

.5403 

.5166 

.4941 

[-180° 

.5966 

.5679 

.5411 

.5171 

.4951 

f-  30° 

.5612 

.5378 

.5147 

.4938 

1/1500 
normal    < 
solution. 

-  60° 

.5612 

.5368 

.5149 

.4938 

-  90° 

.5624 

.5373 

.5149 

.4936 

-120° 

.5630 

.5382 

.5152 

.4931 

-150° 

.5643 

.5382 

.5152 

.4931 

[-180° 

.5650 

.5385 

.5153 

.4938 

f-  60°* 

.5483 

.5257 

.5038 

1/15000 

-  90° 



.5464 

.5338 

.5027 

.4831 

normal    ^ 

-120° 



.5456 

.5233 

.5021 

.4829 

solution. 

-150° 



.5465 

.5234 

.5020 

.4829 

[-180° 

.5476 

.5235 

.5021 

.4828 

The  frequency  interval,  as  may  be  seen  from  table  113,  suffers  a 
marked  change  with  dilution.  The  1/15  and  1/150  normal  solutions 
show  spectral  series  of  86.8  and  85.5  average  interval  respectively, 
the  1/1500  series  of  83.4  units,  the  1/15,000  series  of  only  80.2  units. 
The  1/1500  series  undergo  marked  increase  of  interval  on  cooling. 

The  bands  of  the  1/15,000  normal  are  so  greatly  shifted  that  they  lie 
approximately  in  the  middle  of  the  intervals  between  the  bands  of  the 
1/1500  normal  solution.  Such  a  ''shift"  of  the  entire  spectrum  must 
be  due  to  a  marked  change  in  the  molecular  arrangement ;  hence  it  can 
hardly  be  designated  as  a  shift  of  the  1/1500  normal  spectrum.  Pre- 
sumably a  new  hydrate  has  been  formed  by  the  freezing  of  the  1/15,000 
normal  solution. 

The  1/150,000  normal  solution  gave  a  spectrum  which  was  too  dim 
to  permit  of  measurement,  except  at  the  lowest  temperatures.  From 
the  three  bands  which  are  visible,  it  appears  that  the  frequency  interval 


188 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


is  approximately  77  units.    If  so,  it  is  the  shortest  frequency  interval 
yet  discovered  in  the  fluorescence  of  the  uranyl  salts. 

A  comparison  of  the  location  of  the  bands  of  the  solid  potassium 
sulphate  with  those  of  the  1/15  normal  solution  shows  that  the  bands 
of  the  solutions  are  from  12  to  40  A.u.  nearer  the  red,  according  to  their 
wave-lengths. 

URANYL  POTASSIUM  SULPHATE  IN  SULPHURIC  ACID. 

The  addition  of  sulphuric  acid  in  moderate  proportions  to  the 
aqueous  solutions  of  the  potassium  sulphate  increases  the  intensity 
and  improves  the  resolution  of  the  bands. 

A  solution  of  the  5  c.c.  of  4/15  normal  aqueous  solution  to  1  c.c.  of 
acid  was  subjected  to  the  cooling  process.  In  figures  92  and  93  and 
table  114  the  shifts  will  be  observed.  Band  5,  which  is  typical  of  the 
other  bands,  shifted  toward  the  violet  by  21  A.u.  at  —120°,  and  then 
shifted  6  A.u.  toward  the  red  at  — 180°. 


Fig.  92. — Uranyl  potassium  sulphate — Temperature  shift. 


(1)  1/15  normal,  aqueous;  (2)  1/150  normal,  aqueous;  (3)  1/1500  normal,  aqueous;  (4)  5  c.c.  of  4/15  normal, 
aqueous  to  1  c.c.  sulphuric  acid;  (5)  1  c.c.  of  4/15  normal,  aqueous  to  1  c.c.  sulphuric  acid. 

The  addition  of  acid  in  larger  proportion — 1  c.c.  of  acid  to  1  c.c.  of 
4/15  normal  solution — ^resulted  in  a  spectrum  which  shifted  toward  the 
violet  in  a  peculiar  fashion  with  each  decrement  of  temperature.  (See 
curve  No.  5  of  fig.  92.)    The  total  shift  of  band  5  amounted  to  42  A.u. 

Further  dilution  with  acid,  e.  g.,  20  c.c.  of  acid  to  1  c.c.  of  solution, 
resulted  in  another  broad-banded  spectrum  at  +20°.  With  cooling, 
however,  partial  resolution  occurred.  This  is  best  observed  in  figure 
94,  where  several  narrow  bands  appear  in  the  regions  formerly  occupied 
by  the  broad  bands.    Homologous  components  are  lettered  a,  6,  and  c. 

Still  greater  dilution — 50  c.c.  of  acid  to  1  c.c.  of  aqueous  solution — 
produced  a  spectrum  which  passed  through  the  same  development; 


FKOZEN   SOLUTIONS. 


189 


+2    • 

'    h^-- 

POTASSIUM    SULPHATI  IN  SULPHURIC   ACID. 

9:1 

0* 

^^T\ 

^T\ 

yi\ 

A\ 

-SO' 

XT\ 

A\ 

A\ 

A\ 

-60- 

/T\ 

^T\ 

/\\ 

A\ 

A\ 

-«)• 

>I\ 

yT\ 

y     1  \ 

-^      1    \ 

/J\ 

A\ 

-120' 

^^ 

yn 

/^ 

_/T\ 

A\ 

r\ 

-ISO* 

^^ 

>^ 

A\ 

/]\ 

^ ^  \  v_ 

r\ 

-teo' 

^T\ 

./^ 

XiA 

_yiLV]\ 

/^ 

1 

1 

fsloo 

1 

20I00               1 

.«0i/^ 

.5«l>* 

.Vl\M- 

diLfi.., 

Fig.  93. 


Table  113.- 

—Uranyl  potassium  sulphate  in  water. — 
fluorescence  bands 

Frequencies  and  average  intervals  of 

Band. 

+20" 

0° 

-30° 

-60° 

-90° 

-120° 

-150° 

-180° 

Frequencies 
in  1/15 
normal 
solution. 

3 
4 
5 
6 

7 

1682.9 
1769.9 
1856.7 
1942.5 
2030.0 

1682.1 
1769.3 
1856.7 
1942.5 
2029.6 

1682.1 
1769.0 
1856.6 
1942.5 
2030.0 

1681.8 
1769.0 
1856.3 
1942.1 
2029.2 

1679.8 
1769.0 
1854.3 
1940.2 
2027.2 

1676.2 
1764.0 
1849.8 
1935.7 
2022.2 

1768.0 
1856.0 
1940.2 
2027.6 

1769.6 
1856.3 
1941.0 
2029.2 

Average  int .  . 

86.5 

86.5 

86.8 

86.9 

87.0 

86.9 

86.9 

86.6 

Frequencies 
in  1/150     ^ 
normal 
solution. 

3 
4 
5 
6 

7 

1679.0 
1764.6 
1850.8 
1935.7 
2023.9 

1676.1 
1760.9 
1848.1 
1933.9 
2019.8 

1767.1 
1854.9 
1940.6 
2028.0 

1767.7 
1856.0 
1941.0 
2029.2 

1767.7 
1854.6 
1940.0 
2028.0 

1768.0 
1853.9 
1941.0 
2027.6 

1852.6 
1939.9 

Average  int .  . 

Frequencies   f4 

in  1/1500     15 

normal       ]  6 

solution.      [7 

87.4 

87,0 

87.2 

86.8 

86.5 

86.2 

86.9 

1781.9 
1860.1 
1942.9 
2025.1 

1781.9 
1862.9 
1942.1 
2025.1 

1778.1 
1861.2 
1942.1 
2025.9 

1776.1 
1858.0 
1941.0 
2028.0 

1772.1 
1858.0 
1941.0 
2028.0 

1769.9 
1857.0 
1940.6 
2025.1 

Average  in1 

h 

81.1 

81.1 

82.6 

84.0 

86.3 

86.1 

Frequencies  f4 

in  1/15000    15 

normal       )  6 

solution.      [7 

1823.8 
1902.2 
1984.9 

.1830.2 
1909.1 
1989.3 
2070.8 

1832.8 
1911.0 
1991.6 
2070.8 

1829.8 
1910.6 
1992.0 
2070.8 

1826.2 
1910.2 
1991.6 
2071.3 

Average  ini 

h 

80.6 

79.3 

79.3 

80.3 

81.7 

190 


FLUORESCENCE    OF  THE   URANYL   SALTS. 


+  7* 

jl    UR. POTASSIUM    SULPHATI 

IN   SULPHURIC   ACID. 

• 

1:20 

.--TV 

-38' 

/r\ 

yv\          ^T\ 

/1\ 

-•0° 

y^ 

/n 

/i\     /A 

A\ 

-120" 

yi\ 

/n 

/i\    /n 

h(\ 

-150* 

yyy 

y^ 

/a    jji 

m 

-IM« 

Til 

aAA 

Mi^    -^M 

^ 

leloo 

isloo 

20|00 

.•4|/«' 

.601.^ 

.56|><' 

.521^ 

.481^       , 

Fig.  94. 

hence  it  is  clear  that  the  presence  of  sulphuric  acid  in  excess  is  essential 
to  resolution  of  this  type. 

The  homologous  components  formed  frequency  intervals  which  were 
constant  and  of  the  same  length  as  those  of  the  parent  bands;  i.  e.,  the 
homologous  components  form  separate  series. 

Table  114. — Uranyl  potassium  sulphate  in  sulphuric  add. 


Temp.,  etc. 

Band  2. 

Band  3. 

Band  4. 

Band  5. 

Band  6. 

Band  7. 

6  c.c.  of  4/15  normal  aque- 
ous solution  with  1  c.c. 
of  acid. 

1  CO.  of  4/15  normal  aque- 
ous solution  with  1  c.c. 
of  acid. 

+  20° 
0° 

-  30° 

-  60° 

-  90° 
-120° 
-150° 
-180° 

'+  20° 

-  2° 

-  35° 

-  63° 

-  90° 
-120° 
-150° 
-180° 

0.5392 
.5388 
.5382 
.5379 
.5377 
.5371 
.5373 
.5377 

.5385 
.5378 
.5374 
.5364 
.5362 
.5350 
.5347 
.5343 

0.5150 
.5150 
.5145 
.5142 
.5142 
.5136 
.5139 
.5141 

.5141 
.5142 
.5136 
.5131 
.5127 
.5117 
.5113 
.5107 

0.4931 
.4933 
.4927 
.4928 
.4926 
.4921 
.4926 
.4928 

.4921 
.4918 
.4916 
.4911 
.4908 
.4898 
.4896 
.4892 

0.5650 
.5642 
.5638 
.5635 
.5625 
.5631 
.5633 

.5650 
.5647 
.5635 
.5629 
.5621 
.5611 
.5603 
.5600 

0.5917 
.5917 
.5911 
.5914 
.5917 

0.6219 
.6220 
.6226 

.5946 
.5938 
.5921 
.5915 
.5903 
.5887 
.5885 

.6230 
.6227 
.6211 
.6203 
.6194 

Temp.,  etc. 

Band 
3. 

Band 
4o. 

Band 
5a. 

Band 
56. 

Band 
6a. 

Band 
6&. 

Band 
7a. 

Band 

76. 

1  c.c.  of  4/15  normal  aque- 
ous solution  with  60  c.c. 
acid. 

0° 

-  30° 

-  60° 

-  90° 
-120° 
—150° 
-180° 

3 ! 5966 
.5966 
.5968 
.5979 
.5942 

0.5662 
.5666 
.5662 
.5661 
.5659 

..... 
6! 540] 

0.5388 
.5394 
.5388 
.5387 
.5385 
.5380 
L     .5376 

D!5i58 
.5151 

0.5138 
.5146 
.5141 
.5140 
.5139 

0.4914 
.4916 
.4911 
.4905 
.4902 
.4897 
.4895 



.5 
.5 

663 
634 

)119 
)118 

0.4930 
.4928 

FROZEN    SOLUTIONS. 


191 


io:o 

.601/* 

.52W 

/1\ 

10  :i 

y^ 

/]\ 

x^  /w 

^ 

5:1 

y\ 

/T\ 

/\  /\\ 

^\ 

y^ 

y\ 

/]\ 

/^  y^ 

yi\ 

1:5 

y\ 

.^ 

A\      A\ 

^i\ 

1:20 

^i\ 

/l/^A 

MA               y^A 

/lA 

1:50 

y» 

/\/H/\                 /J\f\ 

AA 

1 

1 

1600 


1800 

Fig.  95. 


2000 


Table  115. 

—JJranyl  potassium  sulphate  in  sulphuric  add- 
intervals  of  fluorescence  bands. 

—Frequencies  and 

average 

Band,  etc. 

+20° 

0° 

-30° 

-60° 

-90° 

-120° 

-150° 

-180° 

Frequencies 

of  5  c.c. 

4/15  normal  - 

aqueous  with 

1  c.c.  acid. 

'2 
3 

4 
5 

6 

7 

1608.0 
1691.8 
1777.8 
1861.9 
1947.0 
2032.1 

1607.7 
1690.9 
1775.9 
1861.2 
1945.9 
2030.0 

1606.2 
1690.0 
1775.3 
1869.8 
1945.1 
2029.2 

1690.0 
1773.7 
1859.1 
1944.8 
2029.2 

1690.0 
1774.6 
1859.8 
1944.8 
2030.0 

1941.7 
2028.0 

1769.9 
1856.0 
1941.7 
2027.2 

1772.4 
1858.0 
1943.6 
2029.6 

Av.  int 

86.7 

85.8 

85.7 

84.8 

84.8 

84.8 

84.5 

84.6 

Band,  etc. 

+20° 

-2° 

-35° 

-63° 

-90° 

-120° 

-150° 

-183° 

Frequencies 

of  1  c.c. 

4/15  normal  - 

aqueous  with 

1  c.c.  acid. 

'2 
3 
4 
5 
6 
7 

1605.1 
1688.9 
1776.5 
1864.3 
1948.9 
2036.2 

1605.9 
1690.6 
1779.0 
1866.0 
1950.5 
2037.5 

1610.0 
1694.1 
1782.2 
1869.2 
1954.3 
2041.7 

1612.1 
1698.7 
1784.8 
1870.2 
1955.8 
2042.5 

1614.5 
1699.2 
1785.7 
1871.6 
1958.1 
2044.2 

'i769!9' 
1857.0 
1945.1 
2032.1 

1681.8 
1770.9 
1859.4 
1944.8 
2033.3 

1684.1 
1774.6 
1860.8 
1947.0 
2034.2 

Av.  int 

87.4 

87.9 

87.5 

86.2 

86.3 

86.3 

86.1 

85.9 

Band,  etc. 

+20° 

0° 

-30° 

-60° 

-90° 

-120° 

-150° 

-180° 

Frequencies 

of  1  c.c. 
4/16  normal  « 
aqueous  with 
60  c.c.  acid. 

'3 

4a 
5a 
56 
6a 
66 
7a 
76 

1676.2 
1766.2 

1676.2 
1766.5 

1675.6 
1767.1 

1672.5 
1765.8 

1682.9 
1774.9 
1851.6 
1860.1 
1941.4 
1953.9 
2029.2 
2042.9 



1766.2 

1764.9 

1856.0 

1853.9 

1856.0 

1856.3 

1867.0 

1858.7 
19.38.7 
1953.6 
2028.4 
2042.1 

1946.3 

1943.3 

1945.1 

1945.6 

1945.9 



2035.0 

2034.2 

2036.2 

2038.7 

2040.0 

Av.  int 

89.6 

89.8 

90.0 

90.6 

91.1 

92.4 

90.0 

192 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


The  effect  of  dilution  with  acid  at  one  temperature  is  given  in  table 
115.  The  —180°  spectra  of  the  4/15  normal  aqueous  solution  with 
varying  proportions  of  acid  are  shown  in  figure  95.  With  the  addition 
of  acid  the  bands  at  first  move  toward  the  violet  without  resolving,  then 
become  stationary  in  position,  and  finally  resolve.  The  ratio  by 
volume  of  aqueous  solution  to  sulphuric  acid  is  given  for  each  spectrum. 
The  shift  is  not  the  same  for  the  different  bands,  because  the  frequency 
interval,  beginning  with  about  85  units  for  the  aqueous  solution, 
increases  with  increase  of  acid  component  to  about  90  units  in  the  50 
parts  acid  to  1  part  water  solution.  With  the  exception  of  the  two 
resolved  spectra,  the  bands  are  too  diffuse  to  permit  of  satisfactory 
intermediate  measurements  on  the  frequency  intervals.  Dilution  with 
acid  has  undoubtedly  increased  the  interval  by  5  units,  whereas  dilu- 
tion with  water  decreased  the  interval  by  8  units. 

URANYL  CHLORIDE  IN  WATER. 

The  absorption  spectrum  of  the  chloride  is  of  particular  interest, 
since  Jones  and  Strong  first  located  absorption  bands^  in  the  fluores- 
cence region  in  an  aqueous  solution  of  this  salt.  Observations  by  the 
authors  on  the  transmission  spectrum  of  several  crystals  of  the  uranyl 
double  chlorides  of  potassium,  ammonium,  rubidium,  and  csesium  have 

Table  116. — Uranyl  chloride  in  water. 


Solution  and  temp.  Band  2.    Band  3.    Band  4. 


0.5 
normal 
solution, 


0.05 
normal 
solution 


0.6247 
.6250 
.6254 
.6255 

.6245 
.6246 
.6252 
.6252 

.6236 
.6249 
.6251 
.6254 


.6253 
.6254 
.6252 


0.5935 
.5940 
.5939 
.5939 

.5931 
.5935 
.5936 
.5934 

.5938 
.5936 
.5933 
.5936 

.5941 
.5942 
.5939 
.5935 


0.5639 
.5644 
.5644 
.5645 

.5643 
.5643 
.5643 
.5642 

.5648 
.5646 
.5646 
.5645 

.5645 
.5647 
.5649 
.5646 


Band  5. 


0.5383 
.5379 
.5379 
.5386 

.5382 
.5382 
.5382 
.5382 

.5385 
.5386 
.5385 
.5382 

.5382 
.5381 
.5381 
.5382 


Band  6. 


0.5142 
.5140 
.5139 
.5143 

.5141 
.5142 
.5141 
.5141 

.5146 
.5144 
.5143 
.5144 

.5144 
.5141 
.5142 
.5144 


Band  7. 


0.4927 
.4925 
.4925 
.4926 

.4926 
.4929 
.4926 
.4926 

.4926 
.4923 
.4924 
.4926 

.4923 
.4923 
.4923 
.4924 


resulted  in  the  discovery  of  absorption  bands  in  the  same  region.  The 
view  held  by  Jones  that  the  fluorescence  spectrum  is  a  continuation  of 
the  absorption  spectrum  is  to  be  gravely  doubted,  for  while  the  chloride 
solution  shows  a  fluorescence  band  at  0.4926  and  Jones  has  established 
the  position  of  an  absorption  band  at  0.4920,  none  of  the  other  bands 

^  Jones  and  Strong.     Carnegie  Inst.  Wash.  Pub.  No.  130,  p.  90. 


FROZEN   SOLUTIONS. 


193 


located  by  him  at  0.6070,  0.6040,  0.6020,  0.6000.  0.5200,  or  0.5185 
coincide  with  a  band  of  the  fluorescence  spectrum.  Furthermore,  it 
has  previously  been  indicated  that  often  the  last  band  of  a  fluorescence 
spectrum  coincides  fairly  well  with  a  strong  band  in  the  absorption. 
It  has  also  been  shown  in  our  study  of  the  fluorescence  and  absorption 
spectra  of  the  crystalline  salts  (see  Chapters  III  to  IX)  that  the  interval 
between  the  absorption  bands,  although  constant,  is  much  smaller 
than  that  between  fluorescence  bands. 

The  bands  of  the  chloride  in  solution  are  separated  by  a  very  black 
background,  but  are  so  dim  that  cooling  to  —90°  is  necessary  before 
measurements  can  be  made.  The  bands  continue  to  increase  in 
brightness  as  the  temperature  is  further  decreased. 

The  temperature  shift  between  —90°  and  —180°  is  toward  the  red 
in  the  spectrum  of  the  3.0  normal  solution.  The  measurements  on  the 
chloride,  to  be  found  in  tables  116  and  117,  indicate  that  difficulty  is 
experienced  in  locating  the  positions  of  the  bands.    The  remarkable 

Table  117. — Uranyl  chloride  in  water — Frequencies  and  average  intervals,  fluorescence  hands. 


Band. 

-97° 

-120° 

-150° 

-180° 

{2 

1600.8 

1600.0 

1599.0 

1698.7 

Frequencies 

3 

1684.9 

1683.5 

1683.8 

1683.8 

in  3.0 

4 

1773.4 

1771.8 

1771.8 

1771.5 

normal 

5 

1857.7 

1859.1 

1859.1 

1856.7 

solution. 

6 

1944.8 

1945.5 

1945.9 

1944.4 

Av.  int .  .  , 

[7 

2029.6 

2030.5 

2030.5 

2030.0 

85.8 

86.1 

86.3 

86.3 

{2 

1601.3 

1601.0 

1599.5 

1599.5 

Frequencies 

3 

1686.1 

1684.9 

1684.6 

1685.2 

in  1.5        ^ 

4 

1772.1 

1772.1 

1772.1 

1772.4 

normal 

5 

1858.0 

1858.0 

1858.0 

1858.0 

solution. 

6 

1945.1 

1944.8 

1945.1 

1945.1 

Av.  int .  .  . 

[7 

2030.0 

2028.8 

2030.0 

2030.0 

85.7 

85.6 

86.1 

86.1 

\2 

1603.6 

1600.3 

1599.7 

1599.0 

Frequencies 

3 

1684.1 

1681.8 

1685.4 

1584.6 

in  0.5 
normal 

4 

1770.5 

1771.2 

1771.2 

1771.5 

5 

1857.0 

1856.7 

1857.0 

1858.0 

solution. 

6 

1943.3 

1944.0 

1944.4 

1944.0 

Av.  int .  .  . 

,7 

2030.0 

2031.3 

2030.9 

2030.0 

86.3 

86.2 

86.2 

86.2 

'2 

1599.2 

1599.0 

1599.5 

Frequencies 

3 

1683.2 

1682.9 

1683.8 

1684.9 

in  0.05 

4 

1771.5 

1770.9 

1770.2 

1771.2 

normal 

5 

1858.0 

1858.4 

1858.4 

1858.0 

solution. 

6 

1944.0 

1945.1 

1944.8 

1944.0 

Av.  int .... 

7 

2031.3 

2031.3 

2031.3 

2030.9 

87.0 

86.4 

86.5 

86.3 

1 

194 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


fact  is  that  the  bands  of  the  1.5,  0.5,  and  0.05  normal  solutions  are  not 
shifted  by  temperature,  and  that  dilution  from  3.0  normal  to  0.05 
normal  produces  a  negligible  shift.  There  is  no  tendency  toward  reso- 
lution. Clearly,  the  uranyl  chloride  in  aqueous  solution  furnishes 
spectra  of  great  stability,  especially  in  view  of  the  behavior  of  the 
bands  of  the  uranyl  nitrate. 

URANYL  NITRATE  IN  WATER. 

The  solutions  of  uranyl  nitrate  present  at  once  the  most  interesting 

and  most  complicated  spectra.    In  our  first  investigations  the  solutions 

were  studied  at  —185°  after  suddenly  plunging  them  into  liquid  air. 

Later  it  became  of  interest  to  study  them  at  several  intermediate 


MITRATE     IN  WATER.                -180° 

m  ^T^    lhyn\  M  /V\    A 

1 

^^T\/K 

./Tv/v    1 

4. 

yi\^/x  /» 

/\Aa        I 

5. 

,__,,! 

L.                  TJy>"T"ATE    IN  WATER.                   -180° 

M. 

/i\^yW/Tx/M^     A 

NITRATC    IN  NITRIC  ACID.  -180^ 

'■"       J\     a/K     a/\     aA 

""         ^        /^        A\/W       AA 

leloo                      1                      2o|oo 

.561^                                      .521^                                              .48U 

Fig.  96. 

temperatures  and  the  freezing  and  subsequent  cooling  was  of  necessity 
done  slowly.  To  our  surprise,  the  normal  solution  of  the  nitrate 
yielded  an  entirely  different  type  of  spectrum.  Spectrum  No.  1  at  the 
top  of  figure  96  represents  the  old  type  and  spectrum  No.  5  the  new 
type.  It  was  found  possible  to  produce  intermediate  degrees  of  resolu- 
tion somewhat  similar  to  Nos.  2,  3,  and  4  by  intermediate  rates  of 
cooling.    The  pertinent  fact  is  that  the  identical  solution  could,  by 


FROZEN   SOLUTIONS. 


195 


manipulation  of  the  cooling  process,  be  made  to  yield  either  an  unre- 
solved or  a  highly  resolved  spectrum.  The  intermediate  forms  were 
not  easy  to  reproduce  at  will.  A  comparison  of  the  wave-lengths  of  the 
strongly  resolved  bands  of  the  solution  at  —180°  with  those  of  the 
crystalline  salt  at  the  same  temperature  showed  that  they  were  identical. 
The  uranyl  ammonium  nitrate  and  uranyl  potassium  nitrate  in 
aqueous  solution  were  similarly  cooled  and  showed  resolution  of  the 
same  type.  Resolution  of  this  type  has  not  been  discovered  in  any 
other  aqueous  solutions,  but  in  our  first  investigation  uranyl  acetate 
in  alcohol  was  found  to  give  highly  resolved  but  quite  dim  bands 
superimposed  on  a  continuous  background.  The  spectra  of  the  1/100 
normal  solution  were  similarly  affected  by  retarding  the  rate  of  cooling. 
Spectra  L,  M,  and  N  of  figure  96  show  the  results  of  successively  slower 
rates  of  cooling. 

EFFECT  OF  TEMPERATURE  ON  SLOWLY  COOLED  SOLUTIONS  OF  URANYL 

NITRATE. 

Since  the  changes  in  the  spectrum  of  the  normal  solution  are  very 
striking  and  are  typical  of  the  changes  in  many  other  more  dilute 
solutions,  a  detailed  account  of  the  changes  in  this  spectrum  is  given. 
Figure  97  gives  a  plot  of  the  spectra.    Some  attempt  at  indicating  the 


NITRATE       IN       WATER 


t20' 


0* 


35' 


-eo* 


JK 


JK 


Jh A 


A. 


■•0* 


-^ 


/\  -    A 


IN   ^ 


A 


J!^ 


M. 


A   K 


-150" 


^ii^ A     I   I ••^ L 


11 


KIQO 


«8|00 


jjfliesL 


•,S*LtL 


.toi^ 


A^UZ 


•S2pr 


^W^ 


Fig.  97. 


form  of  the  bands  is  made,  but  the  changes  in  intensity  are-  too  great 
to  be  represented  on  such  a  plot.  The  wave-lengths  are  tabulated  in 
table  118,  and  frequencies  in  table  119.  At  +20°  only  two  broad  bands 
located  at  0.5323  and  0.5088  were  of  sufficient  intensity  to  be  measur- 


196 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


able.  With  falling  temperature  these  increased  in  brightness  and  two 
more  bands  came  up  to  the  threshold  of  vision.  Bands  0.4890  at  0° 
corresponds  with  an  absorption  band  at  0.4870  discovered  by  Jones 
and  Strong.  The  crystalline  nitrate,  with  6  H2O,  also  has  an  absorp- 
tion band  at  0.4870. 

While  continuing  the  cooling  process  at  a  slow  rate,  a  sharp  rise  in 
temperature  from  —25°  to  —18°  was  invariably  noticed,  probably 
due  to  undercooling  or  change  in  hydration.  Immediately  following 
this  stage  portions  of  the  background  increased  greatly  in  brightness 
so  as  to  broaden  each  band  on  the  violet  side.  These  very  broad  bands, 
which  exist  at  temperatures  between  —25°  and  —40°,  were  found  on 
subsequent  cooling  to  be  the  parents  of  groups  of  resolved  bands.  The 
—40°  bands  were  five  times  the  intensity  of  the  +20°  bands. 

Table  118. — Uranyl  nitrate  in  water — normal  solution. 


Temperature. 

+20» 

0» 

-40° 

-60° 

-90° 

-120° 

-150° 

-180° 

Strong. . 

0.6176 

0.6174 
.6039 
.5856 

0.6161 
.6030 
.6857 
.5829 
.6722 
.6579 
.5553 
.6457 

0.6183 
.6022 
.5861 
.5827 
.5713 
.6577 
.5554 
.5454 

0.6165 
.6006 
.5857 
.5823 
.5712 
.6576 
.5553 
.5455 
.6368 
.6322 
.5299 
.5217 
.5132 
.6089 
.6068 
.5008 
.4991 
.4951 
.4914 
.4855 

Weak... 

Strong. . 

0.5932-0.5696 

.5864 

Weak. . . 

Dim 

.6723 
.5584 

Stromr.. 

0.5622 

.5582 

Dim 

Dim 

.6461 

Dim.... 

Strong. . 
Dim 

0.5323 

.5350 

.5375-0.5182 

.5323 

.5331 
.5299 
.5219 

.6322 
.5300 
.6216 

.5322 
.5299 
.5214 
.6129 
.5090 
.5068 

Dim 

Dim.... 

Strong. . 
Dim. . . . 

.5088 

.5110 



.5129-0.4951 

.6082 

.5093 
.6065 

.5093 
.6069 

Dim 

Dim 

.4924-0.4831 



.4999 

.4997 

.4997 

Dim.... 

Dim 

.4914 
.4857 

.4916 
.4856 

Strong. . 

.4890 

.4862 

.4858 

At  —46°  the  portion  of  each  band  toward  the  violet  decreased  in 
intensity  as  the  part  of  longer  wave-length  became  stronger,  thereby 
tending  to  both  narrow  the  band  and  produce  a  decided  crest.  It  was 
found,  with  the  aid  of  the  spectro-photometer,  that  the  intensity  of  the 
stronger  crest  at  —60°  was  85  times  that  of  the  homologous  band  at 
+20°. 

Further  cooHng  resolved  the  stronger  band  into  doublets  without  a 
real  shift,  but  the  dimmer  component  was  not  so  easily  resolved.  At 
temperatures  between  - 120°  and  - 180°  the  strongly  resolved  doublets 
formed  two  series,  both  of  a  constant  frequency  interval  of  88  units, 
the  single  band  at  0.4885  being  a  member  of  one  series.    There  was 


FROZEN   SOLUTIONS. 


197 


io 


NITRATE   IN  WATKR. 


-30' 


-.:21. 


A ZH A 


A 


.-^ 


JI^ ^s^ 


A 


/i\    ^   /i\^     /a 


H20' 


yL 


A 


.^l\ 


/il 

--:ii LA 


Mi^ 


1 


-150' 


.j^ .-^ 


^H    /Ti 


.ZIL 


i-.   A 


-les" 


-ia /IV7\     ^ 


yr\    A 


y^  » 


^^ 


1 


j^fifi. 


JiififlL 


»9loo 


.60l>t 


r^^ 


T?2k 


^ 


FiQ.  98. 

no  shift  here,  but  increasingly  better  resolution.  The  very  dim  inter- 
mediate bands  resolved  to  form  series  of  approximately  the  same 
interval. 

It  was  thought  that  by  reversing  the  cooling  process  the  spectra 
might  go  through  the  same  forms  at  the  same  temperatures,  which 

Table  119. — Uranyl  nitrate  in  water — frequencies  and  average  intervals  of  fluorescence  bands. 


Band. 

-20*> 

0<» 

-40° 

-60° 

-90° 

-120° 

-160° 

-180° 

3 
4 

6 
6 

i 

Av.int, 

1619.4 

1619.7 
1655.9 

1705.0 

1623.1 
1658.4 

1707.4 
1715.6 
1747.6 

1792.4 
1800.8 
1832.5 

1622.6 
1660.6 

1706.2 
1716.1 
1750.4 

1793.1 
1800.5 
1833.6 

1616.8 
1665.0 

1707.4 
1717.3 
1750.7 

1793.4 
1800.8 
1833.2 

1862.9 
1879.0 
1887.1 
1916.8 

1948.6 
1965.0 
1973.2 
1996.8 
2003.6 
2019.9 

2035.0 
2059.7 

1685.8-1755.6 

1705.3 

1747.3 
1790.8 

1778.7 

1791.6 

1831.2 

1878.6 

1869.2 

1860.5-1929.8 

1878.6 

1875.8 
1887.1 
1916.1 

1879.0 
1886.8 
1917.2 

1879.0 
1887.1 
1917.9 

1949.7 
1964.6 
1973.2 

1965.4 

1956.9 

1949.7-2019.8 

1967.7 

1963.5 
1974.3 

1963.6 
1972.8 

2030.9-2070.0 



2000.4 

2001.2 

2001.2 

2035.0 
2058.9 

2034.1 
2059.3 

2046.0 

2056.8 

2058.6 

86.8 

88.8 

89.8 

87.5 

87.8 

87.2 

87.3 

88.6 

198 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


proved  to  be  the  case  when  the  temperature  was  raised  from  —180° 
to  —60°,  but  on  further  heating  to  —30°  the  —60°  spectrum  failed  to 
change  over  to  the  very  broad  banded  form.  Finally,  the  temperature 
was  raised  to  — 18°,  the  cryohydrate  point.  The  original  spectrum  of 
the  unfrozen  solution  then  reappeared. 


-60' 

~   NITRATE 

IM  WATER. 

y^T\ 

^'TV 

-90' 

^TX 

y^W 

^T\ 

^-TX 

-120* 

y\    ^vk 

/j\    /TX 

yn  .^ 

yiv 

-150' 

A     ^ 

yj/i/rx 

/M^ 

A 

-185" 

/n     y^ 

1^^ 

M/. 

A 

leioo 

1 

leloo 

1 

20100 

I 

••ol^ 

.56|/t 

.52|>* 

.481^ 

Fig.  99. 


The  slow  cooling  of  the  1/10  normal  solution  produced  a  series  of 
spectra  similar  to  the  above,  but  dimmer  and  not  quite  as  well  defined. 
(See  fig.  98.)    The  1/100  normal,  although  too  dim  to  be  measured 


NITRATE       IN    NITRIC   ACID. 


I80' 


20:i 


J .^ 


'  !>*  ^  >^ /n/!tl.L  .A   i«l — AaI  Ia/ii — ^J AaM 


aa I  /^  Ia 


10:1 


/\J^ A. 


I     A    A      AaI   I  A 


Jk A/M  I  A  A 


i-A 


2:1 


J .ax. 


A  A/Ts /T\/\l   lA  A    A AA 


Zl-^a Bi AAI  lA  A I    /1\  Ia 


1:2 


I    ,    •-^ 0- 


u 


Afl_ 


-d[i ZIN^ 


1 


l:2.7S 


/^     A 


^  .  AA  /Aa  /t\ 


JL 


^^TN 


^   A  ^  A  A  A  /^ 


.^ 


.^^TN ^ 


/TA    ^  .^/T^  A    A    A.   A 


..^^IN^ >/-Tx    /^    ^T\ ^i^ 


yn 


.^  /^ 


.^T^ 


••^TN       .^■^"TS r'-T^^. 


teloo 


leloo 


20I00 


'MdL. 


'5g|^ 


.52l>^ 


-iisLif. 


Fig.  100. 


FROZEN   SOLUTIONS. 


199 


until  a  temperature  of  —60°  was  reached,  behaved  similarly.  (See 
fig.  99.)  The  more  dilute  aqueous  solutions,  e.  g.y  the  1/200  and 
1/500  normal,  gave  broad  bands  with  no  important  shifts. 

The  very  dim,  broad  bands  of  the  1/1000  and  1/10,000  normal  are 
probably  due  to  the  production  of  different  hydrates. 
URANYL  NITRATE  IN  NITRIC  ACID. 

The  spectra  of  the  normal  aqueous  solution  diluted  with  nitric  acid 
in  varying  proportion  are  shown  in  figure  100.  Data  for  5  c.c.  of  acid 
are  given  in  tables  120  and  121. 

Table  120. 


Uranyl  nitrate  in  nitric  acid  (1 

c.c.  of  normal  aqueous  solution  with  5  c.c.  of  acid). 

-30° 

-60° 

-90° 

-120° 

-160° 

-180° 

0.6958 
.6818 
.6673 
.5527 
.6399 
.5280 
.6163 
.6046 
.4936 
.4825 

0.6965 
.6806 
.5664 
.6531 
.6393 
.6279 
.6164 
.6043 
.4930 
.4823 

0.5817 

0.5810 

0.6808 
.6681 
.6528 
.5412 
.6274 
.5165 
.6042 
.4941 
.4824 

.  0.6540 

.6540 

.5531 

.5289 

.5283 

.6274 

.5064 

.6047 

.6045 

.4832 

.4823 

Uranyl  nitrate  in  methyl  alcohol 
(0.1  normal  solution). 

Uranyl  nitrate  in  ethyl  alcohol 
(0.1  normal  solution). 

-120° 

-136° 

-150° 

-180° 

-90° 

-120° 

-150° 

-180° 

0.6045 
.5882 
.5780 
.5600 
.5503 
.5341 
.5252 
.6104 
.5025 
.4887 
.4816 

'6]5537' 

.6287 
.6069 

0.5834 
.6557 
.6301 
.5072 

0.6836 
.6652 
.5300 
.6072 

.05788 
.6521 
.6270 
.5040 
.4889 
.4828 

0.5841 
"!5569' 

"']569i" 

"'!4887" 

0.5894 
.5804 
.5605 
.5526 
.5345 
.5272 
.5106 
.5041 
.4887 

0.5891 
.5780 
.5602 
.5610 
.6344 
.5263 
.6108 
.5031 
.4888 
.4819 

The  uppermost  spectrum,  denoted  at  the  left  by  20  :  1,  was  pro- 
duced by  slowly  cooling  to  —180°  and  exciting  to  luminescence  a  solu- 
tion of  20  c.c.  of  the  normal  aqueous  solution  mixed  with  1  c.c.  of  acid. 
The  first  effect  of  the  acid  was  to  bring  out  more  distinctly  the  dimmest 
bands  of  the  aqueous  solution.  There  was  no  marked  shift  or  change 
in  resolution  as  the  acid  component  was  increased  until  the  solution 
contained  1  c.c.  of  normal  aqueous  solution  to  2  c.c.  of  acid.  With 
further  dilution,  e.  g.^  1  c.c.  of  solution  to  2.75  c.c.  of  acid,  a  marked 
change  in  the  spectrum  occurred,  for  only  a  broad-banded  series  of 


200 


FLUORESCENCE   OP  THE    URANYL   SALTS. 


Table  121. — Uranyl  nitrate  in  nitric  acid — Frequencies  and  average  intervals  of 
fiuorescence  hands. 


Frequencies  in  1  c.c.  of  normal  aqueous  with  5  c.c.  of  acid. 

Band. 

-30° 

-60° 

-90° 

-120° 

-150° 

-180° 

2 

3     { 
*     { 

6     / 

7 
Av.int. 

1678.4 

1718.8 
1762.7 

1809.3 
1852.2 

1893.9 
1936.9 

1982.2 
2026.3 

2072.5 

1676.4 

1722.4 
1768.6 

1808.0 
1854.3 

1894.3 
1940.4 

1982.2 
2028.4 

2073.4 



1719.1 

1721.2 

1721.8 
1760.3 

1809.0 

1847.7 

1896.1 
1936.1 

1983.3 
2023.9 

2073.0 

1805.1 

1805.1 

1808.0 

1890.7 

1892.9 

1896.1 

1974.7 

1981.4 

1982.2 

2069.5 

2073.4 

84.8 

87.6 

88.1 

87.8 

88.4 

87.8 



Uranyl  nitrate  in  methyl  alcohol — Frequencies  in  0.1  c.c.  normal  solution 

in  alcohol. 

Band. 

-30° 

-60° 

-90° 

-120° 

-135° 

-150° 

-180° 

2 

•{ 
•{ 

6     1 
6     { 

^  { 

Av.int. 

1654.3 

1700.1 
1730.1 

1785.7 
1817.2 

1872.3 
1904.0 

1959.2 
1990.1 

2046.2 
2076.8 

1712.0 

1966.6 
1723.0 

1784.1 
1810.0 

1870.9 
1896.8 

1958.5 
1983.7 

2046.2 

1697.5 
1730.1 

1785.1 
1814.9 

1871.3 
1900.1 

1957.7 
1987.7 

2045.8 
2075.1 

1795.7 

1880.4 

1964.3 

2046.2 

83.6 

87.4 

87.1 

86.8 

Uranyl  nitrate  in  ethyl  alcohol — Frequencies  in  0.1  c.c.  normal  solution  in 

alcohol. 

Band. 

-90° 

-120° 

-150° 

-180° 

3 
4 
5 
6 

7     ' 

Av.  int. 

1714.1 
1799.5 
1886.4 
1971.7 

1713.5 
1801.2 
1886.8 
1971.6 

1727.7 
1811.3 
1897.5 
1984.1 

2045.5 
2071.3 

1806.0 
1891.4 
1972.8 

83.4 

85.8 

86.1 

85.9 

FROZEN   SOLUTIONS. 


201 


doublets  is  present.  This  is  probably  caused  by  a  change  in  the  hydrate 
at  this  dilution.  This  type  of  spectrum  persisted  through  five  more 
dilute  solutions,  even  when  the  solution  contained  only  1  part  aqueous 
solution  to  1,000  parts  acid. 

The  effect  of  slowly  cooling  five  of  the  acid  solutions  is  seen  in  figures 
101,  102,  103,  104,  and  105. 

Very  often  combinations  of  acid  and  aqueous  solution  proved  to  be 
unstable  on  freezing;  consequently  it  was  difficult  to  reproduce  at 


+  20' 

NITRATE  IN  NITRIC  ACID 

10  :i 

.^ 

^ 

0*                                                                                                                                       ^,^^ 

-SO* 

-•©• 

/1\ 

A 

A 

A 

-»0' 

A 

A 

A 

/k 

M 

.A 

y!\ 

y:\ 

^/\ 

y^y\ 

^  lv{     /\    A 

J 

'ii  ^  A 

J 

L 

A 

-ISO- 

•TV 

A 

/T\ 

^Ih 

A  A 

J 

L. 

J 

\ . 

.1 

-180* 

1 

,  ll 

1    1 

1 

1      1        II 

Ill        M 

1  1      1  1 

uioo 

1 

tsloo 

1 

aoloo 

1 

.601  >* 

.5«\yu 

.52|>* 

.4.1^ 

Fig.  101. 


-o' 

NITRATE  IN 

NITRIC  ACID. 

1:2 

' 

-JO' 

> 

^"T-K 

-45" 

^-- 

-60- 

y\ 

yi\ 

/1\ 

A 

/i\         A 

-90' 

y\ 

y\ 

A 

A 

A         A   . 

-120° 

y\ 

/i\ 

A 

ffi 

Ih         A 

-150' 

yy 

y\ 

M 

/I 

1 

1 

t         .A 

-180"                                                                                      1  1 

1                                1                 .         1      1  1    1                  1 

1,,    , 

III            III 

leloo 

1 

isloo 

1 

20I00                         1 

.60]^ 

.561^ 

.52|>« 

-48|>!Z 

FiQ.  102. 


202 


FLUORESCENCE    OF   THE    URANYL   SALTS. 


-30' 

NITRATE   IN    NITRIC  ACID 

1:3.5 

-60' 

^^-TN 

^TV 

-90* 

y^ 

^ 

/T\ 

/ll 

/T^ 

-120* 

yr\ 

yTvyT\ 

/!vA 

/!l/|\ 

/i^ 

/[V^ 

-150* 

yT\ 

/^A 

y^A 

^ 

/^/l 

/HA 

-leo" 

y\ 

/^/!\ 

/.A 

^/i\ 

/^/^ 

^/^ 

leloo 

1 

isloo 

1 

20IOO 

1 

•^^ 

S6\^ 

.521^ 

•«!'« 

Fig.  103. 

-30° 

NITRATE    IN  NITRIC   ACID.                     1:5 

-«0° 

yn                 yi\                7:1 

A 

/]\ 

-90° 

^         /\        ^ 

/^ 

^ 

-120" 

^  /.    x^  ^   /l/IA  /W  A\ 

A\ 

-ISO" 

yT\      /n     /T\     /^  XTl    /n  /r\ 

/^/n 

A 

-180° 

/T\     >!x   /TV    yK  yi\  y!\  y\\ 

A   /i\ 

A 

leloo 

i              I8I00              1 

20I00 

1 

.60|^                                 .5«|^.                                      .52|^ 

.481^ 

Fig.  104. 


NITRATE  IN  NITRIC    ACID. 


10* 


-30° 


x^y\ 


x^T^ 


.^iza M 


leloo 


1?|oo 


20I00 


■>oU 


.561^ 


j52LfL 


^ 


Fig.  105. 


FROZEN   SOLUTIONS. 


203 


will  the  spectra  of  such  solutions.  This  appeared  to  be  somewhat 
independent  of  the  rate  of  cooling;  thus,  it  was  discovered  that  a  solu- 
tion might  yield  a  spectrum  consisting  of  a,  set  of  broad-banded 
doublets  at  one  time  and  a  narrower  set  of  doul3lets  differently  spaced 
at  other  times.  The  three  spectra  shown  at  the  bottom  of  figure  96 
illustrate  this  phenomenon.  The  first  two  spectra,  although  entirely 
different,  were  produced  from  a  solution  of  1  part  normal  aqueous 
solution  with  10  parts  nitric  acid.  The  first  was  obtained  after  very 
slow  cooling,  the  second  after  moderately  slow  cooling  to  liquid  air. 
The  second  spectrum  is  identical  with  the  third,  obtained  by  slowly 
cooling  a  solution  of  1  c.c.  of  normal  solution  to  3.5  c.c.  of  nitric  acid. 
Such  experiments  lead  to  the  view  that  the  luminescence  spectrum  is 
determined  by  the  particular  hydrate  which  is  formed  on  freezing. 

The  frequency  interval  of  an  acid  or  aqueous  solution  was  always 
constant.  The  change  in  interval  through  a  wide  range  of  dilutions 
was  slight.  The  largest  interval  was  of  87 -f-,  the  smallest  of  84 -h 
units. 


NITRATE  IN  WATER  &  ETHYL   ALCOHOL. 


i:t 


■I20* 


-150* 


-185' 


.Z— 


1^  NITRATE   IN  ALCOH0L;ETHYL. 


150' 


.^ ZH 


185' 


J^    Jh^   ^M 


leloo 


leloo 


zoloo 


sfioLfi. 


seLfl. 


•sal^ 


jlsLfi 


-120* 


<  NITRATE  IN  ALCOHOL  I  METHYL. 
10 


/T\    A\ 


-ZIL 


-135" 


71^ 


A^      Ayr\      AA      a 


-ISO" 


JL 


A,^T>.    yiv^T^    Jiv^-r-^    /iV — ^ 


-185° 


^^      JK  ^^T\       /JV 


A^    A^    A 


-^OL 


«»Iqo 


ibIoo 


20|( 


.60l. 


iSeLfi. 


.521^^ 


r48i^ 


FlQ.  106. 


204 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


THE  URANYL  NITRATE  IN  ALCOHOL. 

The  luminescence  spectrum  of  the  normal  aqueous  solution  diluted 
with  ethyl  alcohol  is  distinctly  different  from  that  of  the  aqeous  solu- 
tion. (See  fig.  106.)  The  sharply  resolved  spectrum  is  quenched  and 
the  new  bands  are  not  in  the  same  positions.  The  unfrozen  solutions  in 
a  mixture  of  alcohol  and  water  are  not  so  opaque  as  the  aqueous 
solutions;  hence  it  is  necessary  to  freeze  them  to  produce  sufficient 
absorption  to  bring  out  the  luminescence.  The  first  readings  were 
taken  when  the  temperature  was  —90°,  and  a  consistent  shift  to  the 
violet  was  effected  by  further  reduction  in  temperature. 

The  spectrum  of  a  solution  of  uranyl-nitrate  crystals  in  ethyl  alcohol 
•will  also  be  found  in  figure  106.  At  -90°,  -120°,  and  -150°  slight 
change  in  form  or  wave-length  occurs,  but  at  — 185°  fairly  well  resolved, 
crests  protrude  above  the  crests  of  the  broad  bands,  still  existent.  It 
is  probable  that  one  series  is  due  to  the  water  of  crystallization,  the 
other  to  the  alcohol.  Jones  and  Strong^  have  attributed  the  presence 
of  two  sets  of  absorption  bands  in  the  water  and  alcohol  solutions  to 
the  presence  of  both  a  hydrate  and  an  alcoholate,  and  the  two  lumines- 
cence spectra  are  undoubtedly  caused  by  such  a  combination. 


Fig.  107. 

A  solution  of  uranyl  nitrate  in  methyl  alcohol  (fig.  106)  presented 
bands  which  in  the  manner  of  development  with  temperature  resem- 
bled the  aqueous  bands.  The  doublets  fall  into  two  series  of  constant 
intervals.  It  will  be  observed  in  figure  106  that  the  bands  of  the  alco- 
holic solutions  are  in  approximately  the  same  positions. 

^  Loc.  cit.,  p.  104. 


FROZEN   SOLUTIONS.  205 

ENERGY  DISTRIBUTION  IN  THE  BANDS  OF  URANYL  NITRATE. 

The  normal  aqueous  solution  at  —90°  was  studied  with  the  aid  of 
the  spectrophotometer  and  bar,  the  intensity  of  the  crests  of  the 
bands  being  matched  by  the  intensity  of  the  acetylene  flame  at  the 
same  wave-length.  These  values  were  multiplied  by  the  ordinates  of 
the  corresponding  wave-lengths  of  the  energy  curve  for  acetylene.^ 
Figure  107  shows  the  manner  in  which  the  bands  differed  in  intensity. 
The  envelope  is  of  the  same  form  as  that  determined  by  Nichols  and 
Merritt^  for  the  individual  bands  of  the  crystalline  salts. 

SUMMARY  OF  CHANGES. 

The  changes  produced  by  slowly  changing  the  temperature  from 
-f-20°  to  -180°  include: 

(1)  An  increase  in  intensity  of  the  entire  spectrum. 

(2)  A  shift  which  is  more  often  toward  the  violet  than  toward 

the  red,  although  both  shifts  may  occur  between  the  above 
temperatures. 

(3)  A  narrowing  of  the  bands  and  in  some  solutions  a  resolu- 
tion of  the  bands. 

(4)  A  slight  change  in  the  frequency  interval. 

(5)  The  formation  of  one  or  more  definite  hydrates. 

(6)  A  change  in  the  form  of  the  bands. 
The  changes  produced  by  dilution  include: 

(1)  A  shift  of  the  entire  spectrum. 

(2)  A  change  of  interval. 

(3)  A  change  in  the  hydrate. 

(4)  A  decrease  in  the  resolution,  excepting  when  small  amounts 

of  acid  are  added  to  an  aqueous  solution. 

(5)  A  decrease  in  intensity. 

CONCLUSIONS. 

(1)  The  constant-frequency  intervals  are  due  to  the  uranium  oxide. 

(2)  The  small  shifts  are  due  to  a  change  in  the  relative  intensity  of 
two  or  more  components  of  a  band. 

(3)  The  more  remarkable  changes  in  position  are  caused  by  the 
presence  of  a  new  hydrate. 

(4)  The  change  in  hydrate  is  probably  often  associated  with  a 
change  in  the  crystal  system,  and  when  this  phenomenon  occurs  a 
change  in  the  grouping  of  the  component  bands  occurs.  The  work 
on  four  double  nitrates'^  (Chapter  VII)  indicates  that  the  crystal 
system  is  an  important  factor  in  the  determination  of  the  positions  of 
the  bands. 

(5)  The  invariable  production  of  broad  bands  with  extensive  aqueous 
dilution  is  due  to  complete  ionization. 

^  Coblentz.     Bureau  of  Standards,  v.  7,  No.  2,  p.  259. 

2  Nichols  and  Merritt.     Physical  Review  (1),  32,  p.  358. 

2  Howes  and  Wilber.     Physical  Review  (2),  xi,  p.  66.     1918. 


NICHOLS 


PLATE  1 


(A)  A  double  reversal  in  uranyl  sulphate  at  185"  C. 

(B)  The  fluorescence  of  uranyl  ammonium  nitrate  at  185°gC. 

(C)  The  polarized  fluorescence  and  absorption  of  uranyl  caesium  chloride  at  185°  C. 
Photographic  reproductions  from  the  original  spectrographs  by  Dr.  R.  C.  Rodgers 


APPENDIX   1. 

CHEMISTRY  OF  FLUORESCING  URANYL  SALTS. 

The  compounds  studied  in  this  work  were  those  uranyl  compounds  which 
showed  a  bright  fluorescence.  These  in  general  were  salts  of  the  stronger 
acids  and  usually  double  salts  with  the  alkali  metals.  The  further  general 
characteristics  were  high  solubility  and  much  water  of  crystallization,  i.  e., 
the  more  water  of  crystallization  the  more  intense  the  fluorescence,  as  in  the 
case  of  the  lithium  manganese  acetates.  The  nonfluorescing  compounds  of 
lower  valence  or  those  without  the  "uranyl"  oxygen,  as  well  as  the  sodium 
carbonate  and  zinconium  oxide  solutions  of  uranic  oxide,  which,  though  having 
peculiar  and  characteristic  absorption,  do  not  fluoresce,  were  not  taken  up. 
The  particular  groups  taken  up  largely  were  the  nitrates,  chlorides,  sulphates, 
and  acetates,  with  potassium,  rubidium,  caesium,  ammonium,  and  sodium  in 
double  salts.  The  phosphates,  fluorides,  oxalates,  and  tartrates  and  some 
double  salts  with  the  bivalent  elements  were  studied  in  some  cases. 

The  material  for  use  in  this  investigation  was  obtained  at  first  from  Kahl- 
baum.  Later  a  number  (25)  of  compounds  were  prepared  by  G.  0.  Cragwall 
in  the  Chemical  Laboratory  of  Cornell  University.  The  remainder  were  pre- 
pared by  the  authors.  Cragwall's  material  was  a  large  quantity  of  uranium 
residue  originally  from  Kahlbaum,  during  the  purification  of  which  by  con- 
version to  ammonium  diuranate  and  hen  to  the  chloride  the  first  ammo- 
nium uranyl  chloride  crystals  with  the  resolved  spectrum  were  observed. 

The  material  used  by  the  author  was  chiefly  uranyl  nitrate  hexahydrate 
purchased  as  chemically  pure,  but  which  was  found  to  contain  noticeable 
quantities  of  sodium  nitrate  crystals.  This  was  dissolved  in  water,  precipi- 
tated with  ammonium  hydroxide,  washed  by  decantation  to  incipient  suspen- 
sion, to  which  HCl  was  added  until  nearly  all  the  precipitate  was  dissolved. 
This  leaves  most  of  the  iron  in  suspension  if  present  in  small  quantities  and  was 
used  to  separate  out  iron  in  reworking  material  contaminated  from  spatulas, 
etc.  On  boiling  this  solution,  if  much  iron  is  present  it  further  coagulates 
and  can  be  filtered,  but  if  the  acid  concentration  is  low  enough,  quite  a  portion 
of  the  uranium  separates  as  H2UO4.  The  chloride  solution  was  precipitated 
again  with  ammonia,  washed,  and  redissolved  in  nitric  acid.  The  nitrate  was 
evaporated  until  the  salt  (trihydrate)  began  to  crystallize  out,  and  was  then 
carefully  heated  until  decomposition  took  place,  with  the  formation  of  the  red 
uranic  oxide.  Care  was  taken  not  to  form  the  black  uranous  uranic  oxide 
U3O8  by  overheating.  The  red  oxide  containing  some  undecomposed  nitrate 
was  digested  with  water,  which  converted  the  oxide  into  the  hydroxide,  or 
acid  H2UO4,  a  bright  yellow  powder.  This  was  washed  free  from  nitrate  by 
decantation  and  air-dried  and  formed  the  major  part  of  the  material  used. 

Some  stock  uranyl  acetate  was  used,  but  as  this  usually  contains  sodium 
acetate  also,  it  is  not  advisable  when  preparing  sodium-free  salts  to  be  com- 
pared with  sodium  triple  salts. 

Some  material  was  also  precipitated  as  the  oxalate,  but  this  does  not  give 
complete  precipitation,  and  as  it  gives  the  black  UaOg  on  ignition,  which  is 
not  as  readily  soluble,  it  is  not  of  much  value  except  for  preparing  oxalates. 

207 


208 


FLUORESCENCE    OF   THE   URANYL    SALTS. 


For  making  triple  sodium  acetates,  some  material  was  precipitated  as  the 
sodium  uranate,  dissolved  in  sodium  carbonate,  and  the  solution  treated  with 
acetic  acid,  from  which  the  sodium  uranyl  acetate  crystalUzes,  leaving  the 
sodium  acetate  in  solution  with  very  little  waste  uranyl  salt. 

NITRATES. 

URANYL  NITRATE. 

This  is  the  commonest  and  best  known  of  the  uranyl  salts,  crystallizing 
ordinarily  as  the  hexahydrate,  which  readily  forms  large,  clear  crystals  by 
coohng  or  evaporation.  It  is  prepared  by  dissolving  either  the  uranic  oxide 
or  hydroxide  H2UO4  or  the  uranous  uranic  oxide  UaOs  in  nitric  acid  and  crystal- 
Uzing.  This  salt  shows  strikingly  the  property  of  most  of  the  uranyl  salts 
of  strong  acid,  of  dissolving  noticeable  amounts  of  the  oxide  in  the  neutral 
solution,  so  that  a  clear  solution  may  be  strongly  basic.  This  oxide  pre- 
cipitates on  heating  or  evaporation. 

Uranyl  Nitrate  Hexahydrate. 
U02(N03)26H20. 

The  complete  description^  of  the  crystal  properties  of  this  hydrate  are  given 
in  Groth's  Chemische  Krystallographie,  II,  page  142. 

System  rhombic;  axial  ratio  a:h:c  =  0.8737: 1:  0.6088.  Forms  h  (010), 
a  (100),  making  short  rectangular  prisms  with  pyramidal  ends  formed  by 
b  (111),  usually  cut  also  by  5  (Oil),  making  a  a  six-sided  face  and  h  eight- 
sided.  The  prism  (110)  was  observed  on  one  crystal  which  was  deformed  by 
growing  near  another.  Specific  gravity,  according  to  Boedeker  (1860),  is 
2.807. 

No  statement  is  made  as  to  cleavage,  but  it  was  found  that  very  shght 
temperature  changes  produce  a  spontaneous  cleavage,  generally  along  5  (Oil), 
so  that  the  crystals  can  not  be  handled  on  a  cold  day  and  immersion  in  liquid 
air  completely  powders  them. 

The  optical  properties  are  double  refraction  +,  plane  of  axes  h  (010),  acute 
bisectrix  the  c  axis,  apparent  angle  of  optic  axes  67°  to  69°,  mean  index 
jS  1.495  to  1.502.  The  pleochroism,  according  to  Schabus,  gives  bright  yel- 
low-green parallel  to  a,  h  greenish  yellow,  c  deep  citron  yellow. 

The  fluorescence  and  absorption  were  investigated  by  Stokes^,  E.  Becquerel, 
Hagenback,^  and  H.  Becquerel.^  The  tribo-luminescence  was  noticed  by 
Herschel.^  Wasiljew^  gives  the  melting-point  of  the  hexahydrate  as  60.2°  C. 
and  gives  the  solubiUty  curve  for  the  hexahydrate  in  water.     Silliman'  gave 

1  de  la  Provostage,  Ann.  der  Chim.  Phys.  (3),  5,  48.     1842. 

Schabus,  Preischr.  Wien  (1855),  40. 

Sitz.  berichte  d.  A.  d.  W.  Wien,  27,  41.     1857. 

Rammelsberg,  Neust.  Fortsch.  in  de  Kryst.  Chem.  Leipzig,  58.     1857. 

Lang,  Sitz.  ber.  Wien,  31,  120.     1858. 

des  Cloiseau,  Annales  des  Mines  (5),  14,  348.     1858. 

Quercigh,  Riv.  Min.  crist.  Ital.,  4,  6-14.     1915. 
'  Stokes,  Phil.  Trans.,  142,  517,  520.     1852. 
3  Hagenback,  Poggendorff's  Annalen,  146,  395.     1872. 
*  H.  Becquerel,  Ann.  Chim.  Phys.  (6),  14,  230.     1888. 
^  Herschel,  Nature,  60,  29.     1899. 
"Wasiljew,  Chem.  Zentralblatt  14,  2,  ii,  1527.     1910.     Jour.  Russ.  Phys.  Chem.  Ges.  42, 

577.     1910. 
'Silliman,  Amer.  Jour.  Science  (2),  27,  14.     1859. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  209 

59.5°  C.  which  is  probably  not  as  accurate.  Lowenstein^  gives  the  vapor- 
pressure  of  the  saturated  solution  as  18  mm.  approximately  at  25°  and  the 
pressure  of  the  equilibrium  between  hexahydrate  and  trihydrate  as  over 
4  mm.  The  author  found  the  two  hydrates  to  be  stable  together  at  5  mm.  at 
20°.  The  result  is  that  the  crystals  always  effloresce  and  fall  to  a  yellow 
powder  if  left  in  the  air,  in  the  winter  especially  if  the  sun  falls  on  them,  and 
may  deliquesce  in  the  summer.  Lescouer^  gives  the  vapor-pressure  of  the 
solution  at  6°  as  12  mm.  and  for  the  trihydrate  below  3  mm.  The  author 
found  that  the  hexahydrate  dissolved  in  various  concentrations  of  nitric  acid 
at  20°  C.  in  the  following  ratio:  1.6  grams  of  hexahydrate  in  1  gram  of  10  per 
cent  HNO3,  1.15  grams  in  20  per  cent,  0.8  gram  in  30  per  cent,  0.65  gram  in 
40  per  cent  to  70  per  cent  HNO3.  The  values  have  not  been  determined 
accurately  above  40  per  cent  on  account  of  the  compHcations  due  to  the 
occasional  formation  of  the  trihydrate. 

These  crystals  were  usually  grown  by  evaporation  in  the  room.  For  work 
on  the  polarization  they  were  grown  in  thin  plates  tabular  on  a  or  6  by  putting 
small  seed  crystal  in  a  solution  of  the  depth  desired  for  the  thickness  of  the 
crystal,  in  the  position  desired. 

Ukanyl  Nitrate  Trihydrate. 
U02(N03)23H20. 

This  hydrate  is  mentioned  by  Lescouer^  and  by  Ditte*  as  being  formed  when 
the  hexahydrate  is  heated  to  boiUng.  Drenkman^  and  Schultz-Sellack^  found 
that  on  adding  the  hexahydrate  to  strong  nitric  acid  and  crystalhzing  by  cool- 
ing or  evaporation  the  trihydrate  was  obtained.  Lebeau^  also  obtained  it 
by  heating  the  hexahydrate  on  the  water-bath  or  by  evaporating  the  nitric 
acid  solution  in  a  dessicator  over  H2SO4  or  KOH.  Marketos^  mentions  it  as 
formed  directly  from  the  hexahydrate  over  sulphuric  acid  in  a  dessicator,  as 
does  also  Forcrand.^  As  can  be  deduced  from  the  vapor-pressure  data  of 
Lowenstein  and  the  author,  this  air-drying  takes  place  as  soon  as  the  vapor- 
pressure  of  the  water  in  the  atmosphere  goes  below  5  mm.  The  best  crystals 
are  obtained  by  slow  evaporation  of  the  solution  of  the  hexahydrate,  dried  on 
the  water-bath  in  concentrated  nitric  acid  in  a  dissicator  over  sulphuric  acid 
and  caustic  potash  or  quickhme. 

The  crystalline  form  was  measured  by  G.  Wyrouboff,^"  who  obtained  his 
crystals  by  evaporating  the  neutral  solution  at  65°. 

System  triclinic;  axial  ratio,  a  :b  :  c=  1.7753:      1:1.  4104. 

a  85°35';  i8_94°12';  7  81°44'. 

Forms  p  (001),  making  plates  with  h'  (100),  a'  (101),  and  a*  (201)  on  the 
edges,  and  c*  (HI)  and  6*  (111)  obHque-angled  ends. 

The  specific  gravity  was  found  to  be  3.345.  No  cleavage  has  been  noticed, 
although  the  crystals  are  likely  to  form  with  irregular  cracks  across  or  radiat- 

1  Lowenstein,  Zeit.  Anorg.  Chem.  63,  105-107.     1909. 

2  Lescouer,  Ann.  China.  Phys.  (7),  7,  429.     1896. 
'  Lescouer,  loc.  cit. 

*  Ditte,  Ann.  Chim.  Phys.  (5),  18,  337.     1879.     Compt.  Rend.  89,  643.     1879. 

5  Drenkman,  Jahrsber  der  Fortschritt  Chem.,  256.     1861. 

8  Schultz-Sellack,  Jahrsber.  Fort.  Chem.,  365.     1870;  Zeit.  fur  Chem.,  646.     1870. 

7  Lebeau,  BuU.  Soc.  Chim.  (4),  9,  299.     1911. 

8  Marketos,  Comptes  Rendus,  155,  210.     1912. 

»  Forcrand,  Comptes  Rendus,  156,  1044,  1207,  1954.     1913. 
10  Wyroubofif,  Bull.  Soc.  fran.  Mineral,  32,  340.     1909. 


210  FLUORESCENCE    OF   THE    URANYL   SALTS. 

ing  from  the  seed.  Schultz-Sellack  gives  the  melting-point  as  120°  and 
Wasiljew  as  121.5°  C.  It  is  really  only  a  partial  melting-point,  as  the  dihy- 
drate  is  not  completely  soluble  in  the  resulting  solution.  The  solubility  of  the 
trihydrate  in  water  above  60°  or  in  nitric  acid  has  not  been  determined, 
although  Ditte  gives  a  solubiUty  of  14.39  parts  of  the  trihydrate  in  mono- 
hydrated  (91  per  cent)  nitric  acid. 

Uranyl  Nitrate  Dihydrate. 
U02(N03)22H20. 

Ordway  describes  the  dihydrate  as  resulting  by  boihng  off  the  fused 
hexahydrate,  which  Lowenstein  confirms.  The  latter  finds  it  as  the  product 
of  6  days'  dihydration  over  sulphuric  acid  of  over  80  per  cent  strength,  al- 
though Fourand  finds  6  days  required  in  a  vacuum  over  strong  sulphuric. 
Lebeau  finds  powdered  hexahydrate  converted  to  dihydrate  in  a  vacuum  desic- 
cator with  concentrated  sulphuric  acid  in  72  hours.  Lebeau  finds  that  on 
treating  the  hexahydrate  with  ether,  two  layers  are  formed,  of  which  the 
ethereal  layer  can  be  dried  with  anhydrous  calcium  nitrate,  which  leaves  the 
dihydrate  on  evaporation.  It  is  to  be  noted  in  this  connection  that  the  ethereal 
solution,  which  is  also  used  for  separating  uranium  X,  can  not  be  boiled  off,  as 
it  decomposes  with  explosive  violence  after  some  heating,  liberating  copious 
nitrous  fumes. ^  Lebeau  also  obtains  crystals  with  ether  of  crystallization  at 
10°  and  —70°.  The  dihydrate  may  also  be  formed  by  adding  dry  UO3  to 
fuming  nitric  acid  (92  per  cent),  from  which  solution  it  is  readily  recrystal- 
lized.  Wasiljew,  crystalHzing  the  dihydrate  from  fuming  nitric  acid  (s.  g. 
1.502),  finds  quadratic  tables  of  the  rhombic  system  with  strong  fluorescence. 
The  author  found  yellow  plates  with  marked  fluorescence  at  lower  tempera- 
tures of  probably  rhombical  pinacoid  and  pyramid,  with  some  other  forms. 
The  crystals  weather  so  rapidly,  having  a  vapor-pressure  of  0.2  mm.,  accord- 
ing to  Lowenstein,  that  changing  from  one  closed  vessel  to  another  usually 
tarnishes  them  so  that  Httle  can  be  done  in  the  way  of  measuring,  handhng  for 
cleavage,  etc.  Wasiljew  gives  the  melting-point  as  179.3°.  The  mixture  of 
dihydrate  and  solution  obtained  by  melting  the  trihydrate  goes  over  to  solu- 
tion at  about  160°  and  then  goes  unchanged  except  for  slight  boihng  to  240°. 

Uranyl  Nitrate  Anhydrous. 
U02(N03)2  or  UO3.N2O5. 

Marketos  produced  anhydrous  uranyl  nitrate  by  heating  the  nitrate  to  170° 
to  180°  C,  since  total  decomposition  took  place  at  200°,  and  passing  over  it 
dry  carbon  dioxide  saturated  with  nitric-acid  vapors  by  bubbling  through 
concentrated  nitric  and  sulphuric  acids.  This  produced  a  yellow  amorphous 
salt  soluble  in  water  which  decomposed  ether,  with  the  liberation  of  nitrous 
vapors.  Forerand  found  that  long  heating  above  125°  C.  in  a  current  of  dry 
carbon  dioxide  produced  basic  anhydrous  nitrate  and  below  100°  only  a 
monohydrate.  Twelve  hours  at  165  in  a  current  of  carbon  dioxide  charged 
with  nitric-acid  vapors  gave  U02(N03)2  +  I/3IH2UO4. 

The  method  evolved  for  producing  anhydrous  uranyl  nitrate  was  to  place 
in  a  train  of  U -tubes  a  tube  containing  uranic  oxide  made  by  heating  the 
hydroxide  or  acid  H2UO4  until  it  began  to  turn  red  and  distilling  over  it  nitric 

1  Muller,  Chem.  Ztg.,  41,  439,  1917;  40,  30,  1916. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  211 

anhydride,  N2O5.  This  was  accomplished  by  having  a  reaction  flask  fitted 
to  the  system  by  a  ground-glass  joint,  in  which  were  placed  phosphorus 
pentoxide  and  fuming  (92  per  cent)  nitric  acid  in  calculated  amounts.  From 
this,  on  heating  to  50°,  the  N2O5  distilled  out  and  was  condensed  by  freezing 
mixture  in  the  first  U-tube,  which  served  as  a  reservoir.  When  this  was 
filled  with  solid  N2O5  and  a  two-hquid  layer  of  N2O6  and  HNO3,  the  flask  was 
removed,  the  joint  covered  by  a  cap,  and  the  anhydride  distilled  over  on 
the  uranic  oxide  by  placing  the  reservoir  tube  in  a  bath  of  hot  oil.  No  re- 
action took  place  between  the  oxide  and  the  acid  until  the  oxide  tube  was  in 
turn  put  in  the  oil-bath  and  the  anhydride  boiled  off  into  the  last  tube,  which 
served  as  a  second  reservoir  for  the  acid.  As  soon  as  the  acid  began  to  boil 
the  reaction  took  place,  producing  a  vivid  green  fluorescence  and  a  fight  yel- 
low color  instead  of  the  reddish  oxide.  The  anhydride  could  be  distilled  off 
and  run  back  over  while  holding  the  tube  with  the  uranyl  nitrate  at  any 
temperature.  Also,  any  acid  which  did  not  solidify  could  be  poured  off  and 
the  remaining  N2O5  run  back  over  the  nitrate,  insuring  absolute  freedom  from 
water.  The  resulting  compound  was  found  to  be  stable  up  to  180°,  at  which 
temperature  it  broke  up  into  N2O5  and  UO3,  which  could  be  recombined  if  the 
temperature  was  lowered.  Distilfing  the  acid  on  and  off  was  performed 
several  times  with  one  specimen,  examining  the  spectra  each  time,  which 
showed  first  the  anhydrous  salt  fluorescence  and  then  none  for  the  oxide. 

DOUBLE  NITRATES. 

Meyer  and  WendeP  prepared  double  salts  of  ammonium,  potassium,  rubi- 
dium, caesium  nitrates  with  uranyl  nitrate.  These  crystals  were  described  by 
Steinmetz.^  They  were  grown  from  a  solution  in  nitric  acid  and  were  of  the 
type  KU02(N03)3.  Rimbach^  endeavored  to  determine  the  solubihty  of  these 
salts  in  water  at  various  temperatures.  He  found  large  crystals  in  the  am- 
monium and  potassium  solutions  unlike  those  of  Meyer  and  Wendel  which 
were  measured  by  Sachs^  and  assigned  formulae  Uke  those  of  Meyer  and  Wen- 
del,  but  since  they  were  ahke  were  called  isomorphous  and  the  a  forms  of  NH4 
and  KU02(N03)3.  Examination  of  the  spectra  of  these  forms  in  the  labora- 
tory indicated  and  Sachs's  data  itself  proves  that  the  a  form  is  simply  uranyl 
nitrate  hexahydrate. 

In  attempting  to  grow  crystals  according  to  Rimbach's  method  which  would 
not  be  uranyl  nitrate,  however,  two  new  forms  were  discovered  containing  two 
molecules  of  alkaU  nitrate  to  one  of  uranyl  nitrate.  In  the  process  of  growing 
the  potassium  salt  for  experimental  purposes,  still  a  third  was  found,  but  so 
rarely  that  it  was  not  studied. 

In  order  to  find  out  the  conditions  under  which  the  various  salts  were  formed, 
a  series  of  solubihty  determinations  were  undertaken,  being  run  at  constant 
temperature  of  20°  C.  in  a  thermostat,  with  varying  percentages  of  aqueous 
nitric  acid  as  a  solvent. 

From  these  incomplete  results  it  will  be  seen  that  from  solutions  of  less 
than  30  per  cent  nitric  acid  and  less  than  1  molecule  of  uranyl  nitrate  to  1  of 
potassium  nitrate,  potassium  nitrate  only  will  crystalUze;  that  in  a  1  to  1 

1  Meyer  and  Wendel,  Ber.  d.  d.  Ch.  Ges.,  36,  4055.     1903. 

2  Groth's  Chem.  Kryst,  11,  150. 

'  Rimbach,  Ber.  d.  d.  Ch.  Ges.,  37,  472.     1904. 
*  Sachs,  Zeit.  f.  Krys.,  38,  497.     1904. 


212 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


solution  above  40  per  cent  the  so-called  7  form  or  monopotassium  salt  will 
appear.  In  the  1  of  uranyl  nitrate  to  2  of  potassium  nitrate,  the  double 
nitrate  crystalHzes  only  above  50  per  cent  of  nitric  acid,  and  as  the  5  phase  or 
the  dipotassium  salt  and  the  metastable  phase  at  this  concentration  is  the  7 
form.  Presumably  at  higher  concentrations  of  potassium  nitrate  the  last- 
found  and  undetermined  form  would  appear. 


Grams 

of  solute  in  100  grams  0 

/  solvent. 

Solvent 
(p.  ct.  HNOs). 

KN03.U02(N03)2. 

2KN03.U02(N03)2. 

KNO3. 

0             .    . 

85.5 
82.0 
99.8 
89.0 
81.3 
54.0 
33.9 

Solid 
phase. 
KNO3 
KNOs 
KNO, 
Hex 

y 
y 
y 

Solid 
phase. 

62.9 
52.2 
45.7 
51.8 
67.2 
52.3 

Solid 
phase. 
KNO3 
KNOs 
KNO3 
KNOs 
KNO3 
8 

Solid 

31.4 
19.1 
14.5 
11.4 
15.2 
18.6 
19.6 
29.6 
34.2 
48.8 

10         



20 

30 

89.5 

y 

40 

60 

57.5 

y 

60 

70 

80 

90 

Solvent 
(p.  ct.  HNOs). 

NH4NOs.U02(N03)2. 

2NH4N03.U02(N03)2. 

NH4.NO8 

0 

165 

128.6 
80.3 
68.2 
60.5 
61.4 
38.6 

Solid 
phase. 

Hex. 

Hex. 

Hex. 

Hex. 

Hex. 

/3 

Solid 
phase. 

251 

201 

150 

144 
98.2 
58.0 
35.6 

Solid 
phase. 
Hex. 
Hex. 
Hex. 
Hex. 

/3 

380 
380 
215 
150 

Solid 
phase. 

191 

151 

127 

104.8 
86.4 
76.5 

10             

20 

144.5 
144 
95.6 

/3 

30 

40 

60 

60 

Solid  phases  appearing  are: 
Potassium  nitrate,  KNO3. 
Ammonium  nitrate,  NH4NO3. 

Uranyl  nitrate  hexahydrate,  U02(N03)2  6H2O,  Hex. 
Monopotassium  uranyl  nitrate,  KU02(N03)3,  7. 
Dipotassium  uranyl  nitrate,  K2U02(N03)4,  8. 
Monoammoniimi  uranyl  nitrate,  NH4U02(N03)3,  /3. 

From  solutions  1  molecule  of  uranyl  nitrate  to  1  of  ammonium  nitrate, 
uranyl  nitrate  hexahydrate  crystallizes  unless  the  per  cent  of  nitric  acid  is  at 
least  50,  above  which  the  ^  or  monoammonium  form  crystalUzes,  which  is 
metastable  practically  to  water  solution.  From  2  molecules  of  ammonium 
nitrate  to  1  of  uranyl  the  hexahydrate  crystallizes  up  to  40  per  cent,  above 
which  the  /3  form  appears,  which  is  also  metastable  to  pure  aqueous  solution. 
It  will  be  noted  that  while  potasisum  nitrate  is  about  as  soluble  as  uranyl 
nitrate  and  the  phase  in  equilibrium  with  the  more  acid  solutions  corresponds 
to  the  composition  of  the  solution,  the  ammonium  nitrate  is  much  more  solu- 
ble and  not  only  does  not  form  the  sohd  phase  in  case  uranium  is  present, 
but  does  not  form  the  diammonium  salt  from  solutions  of  that  composition. 
Laboratory  experience  showed  that  a  large  excess  of  ammonium  nitrate  and 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  213 

rather  low  acid  concentration  was  necessary  to  produce  this  form.  These 
higher  ratios  of  ammonium  nitrate  should  be  investigated. 

These  results  do  not  check  well  with  those  of  Rimbach,  who  presumably 
crystallized  considerable  portions  of  the  salt,  instead  of  determining  the  phase 
with  which  the  solution  was  in  equilibrium  by  the  addition  of  seeds  of  known 
phases.  They  do  not,  however,  materially  conflict  with  those  of  EngeP  in  the 
case  of  the  solubiUty  of  potassium  nitrate  in  nitric  acid,  where  the  solubility 
is  found  greater  at  20°  than  at  0°  in  dilute  solutions  and  less  in  highly  acid 
solution. 

The  mono  or  acid  forms  of  the  double  potassium  ammonium  salts  and  the 
corresponding  rubidium  and  caesium  salts  were  found  to  be  as  described  by 
Sacks  from  the  preparation  of  Meyer  and  Wendel.  There  is  no  indication 
that  the  corresponding  double  salts  containing  2  atoms  of  rubidium  or  caesium 
could  not  be  produced  by  using  solutions  similar  to  that  used  for  the  dipotas- 
sium  salt. 

Other  double  uranyl  nitrates  with  other  bases  than  the  four  alkaUes  dis- 
cussed do  not  seem  to  form,  with  the  exception  of  thalHum,  which  is  reported 
by  Meyer  and  Wendel  as  forming  but  being  non-fluorescent,  as  the  double 
thallous  sulphate  is.  Sodium  nitrate  crystalhzes  side  by  side  with  the  hexa- 
hydrate  or  trihydrate,  according  to  the  acidity  of  the  solution,  but  no  con- 
ditions were  found  under  which  the  two  salts  would  crystalhze  together. 
Silver,  cadmium,  zinc,  calcium,  barium,  and  magnesium  were  also  tried  with- 
out success,  although  a  modification  of  the  hexahydrate  spectrum  was  pro- 
duced by  the  calcium  and  magnesium.  Meyer  and  Wendel  also  tried  hthium, 
sodium,  and  the  bivalent  metals  without  formation  of  double  salts. 

MoNOPOTASsiuM  Uranyl  Nitrate. 
(t  form)  KU02(N03)3. 

These  crystals  were  prepared  by  Meyer  and  Wendel  by  crystaUizing  potas- 
sium nitrate  and  uranyl  nitrate  in  equal  proportions  from  a  nitric-acid  solu- 
tion.   The  crystals  were  examined  by  Steinmetz. 

System  rhombic;  axial  ratio  0.8541 : 1 :  0.6792. 

Thick  tabular  combinations  of  c  (001),  m  (110),  with  subordinate  forms  of 
h  (010),  s  (102),  o  (111),  sometimes  a  (100),  and  rarely  a  (Oil)  and  122. 
Steinmetz  and  Sykes  report  good  cleavage  on  h,  and  good  cleavage  was  also 
observed  on  a.  The  specific  gravity  was  found  to  be  3.503.  Crystals  of  this 
form  are  stable  at  20°  if  the  partial  pressure  of  the  water-vapor  is  not  over 
9  mm.  Hg,  but  at  that  point  begin  to  deUquesce,  changing  to  a  whitish  yel- 
low chalky  mass.  On  heating  the  crystals,  yellow  crusts  begin  to  form  on  the 
crystals  at  150°,  violent  decrepitation  begins  at  200°,  and  decomposition  with 
hberation  of  nitrous  fumes  at  270°  C. 

According  to  Steinmetz,  the  plane  of  the  optical  axes  is  c  (001),  acute 
bisectric  a.    Axes  visible  through  (110). 

The  best  crystals  were  obtained  by  cooHng  of  hot  solutions  supersaturated 
2  grams  in  50  c.c.  in  glass-stoppered  bottles. 

The  composition  as  determined  by  Meyer  and  Wendel  was  KU02(N03)3. 
An  ignition  run  to  check  this  gave  65.13  and  64.82  per  cent,  the  theoretical 
form  K2U2O7  being  67.29,  the  low  values  being  due  to  loss  by  decrepitation. 

1  Engel,  Comptes  Rendus,  104,  913.     1887. 


214 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


DiPOTASSiuM  Uranyl  Nitrate. 
(5  form)  K2U02(N03)4. 

These  crystals  appeared,  after  a  year  of  effort  to  obtain  crystals  from  neutral 
solution  which  were  not  hexahydrate,  in  a  slightly  acid  solution  containing  an 
excess  of  potassium  nitrate.  It  shows  marked  reluctance  to  appear  and  does 
not  grow  well  if  the  room  temperature  is  below  20°  C,  the  hexahydrate  forming 
instead,  but  above  that  temperature  gives  fine  crystals,  especially  if  seeded, 
although  it  does  not  grow  as  rapidly  as  the  other  members  of  the  group. 

System  monoclinic;  axial  ratio  a  :h:  c  =  0.6394  : 1 :  0.6190;  i3  =  90±. 


calc. 

ohs. 

calc. 

obs. 

c:a  =001 

:  1 00  = 

90°    0' 

O'.TT  =133 

:  232  =19°  19' 

20°  44' 

p:p'=331 

•  331  = 

63°  30' 

o:q  =133 

131=52°    3' 

51°  50' 

c:p  =001 

:  331  = 

77°  38' 

Old  =133 

:  101  =45°  38' 

47°  35' 

c:d  =001 

:  101  =50°    V 

62°  52' 

P.-TT    =331 

:  232  =23°  39' 

22°  49' 

c:o  =001 

133  =42°  43' 

43°  10' 

p:d  =331 

:  101  =38°  42' 

38°  25' 

c:q  =001 

:  131  =59°  22' 

60°  39' 

p:q  =331 

:  131  =43°  37' 

42°  12' 

o:o  =133 

:  133  =73°  58' 

73°  15' 

d:q  =101 

:  131  =56°  31' 

56°  17' 

o:p  =133 

:  331  =42°  58' 

42°  48' 

d'.T  =101 

:  232  =37°    6' 

38°  56' 

o:p'=133 

:  331  =84°  19' 

84°    0' 

d:m=101 

:  230=61°    7' 

62°  48' 

These  axes  are  probably  not  those  of  the  space  lattice,  being  taken  from 
the  first  habitus  observed,  which  formed  in  a  solution  having  barely  enough 
potassium  nitrate  to  produce  this  phase,  and  consisted  of  e  (001),  o  (133),  and 
p  (331)  meeting  in  a  point  in  front  which  was  sometimes  cut  off  by  a  (100), 
usually  accompanied  by  d  (101).  tt  sometimes  occurred  between  o  (133) 
and  p  (331)  and  q  (131)  between  o  133  and  p  311;  6  (010)  and  m  (230)  were 
found  in  measurement.  One  crystal  showed  c,  o,  p,  d,  and  d'  (101),  a  and 
probably  q  and  (111).  Most  of  the  crystals  grown  later  had  a  prismatic  or 
needle  habitus  in  which  p  (331)  was  the  predominant  form,  with  small  e 
faces  on  the  ends  and  occasionally  some  of  the  other  forms.  All  faces  on  these 
crystals  gave  reflections  which  appeared  in  the  goniometer  as  a  flattened 
figure  8,  and  best  agreements  were  found  in  the  angles  taken  from  the  outside 
of  every  pair  of  readings.  In  case  the  whole  figure  did  not  appear,  results 
were  unsatisfactory. 

On  dissolving  a  large  crystal  in  the  mother-liquor  by  heat,  c  (001)  was  un- 
touched, d  (101)  was  left  even  and  a  little  pitted,  and  the  edge  between  p  (331) 
and  b  (133)  was  rapidly  dissolved,  leaving  the  deepest  etching  where  these 
met  at  d  (101). 

No  conspicuous  cleavage  was  noticed. 

The  specific  gravity  was  found  to  be  3.359. 

On  heating  crystals  of  this  phase,  they  first  decrepitate  to  an  opaque  yellow 
powder  at  200°  C.,  which,  at  260°  C,  fiows  together.  Above  this  temperature 
decomposition  sets  in,  with  the  evolution  of  nitric  fumes.  Various  colored 
masses  result,  deep  red  UsOs,  bright  red  UO3,  bright  yellow  K2UO4,  and  on 
cooling  a  beautiful  rose  pink  pervades  the  mass. 

This  phase  does  not  change  over  concentrated  sulphuric  acid,  ^.  e.,  has  zero 
vapor-pressure  at  20°  C,  but  over  acid  corresponding  to  11  mm.  of  mercury 
of  partial  pressure  of  water-vapor  it  turns  whitish  without  becoming  moist, 
probably  due  to  the  formation  of  KNO3  and  U02(N03)2  6H2O.  This  is  the 
same  pressure  at  which  the  diammonium  salt  deUquesces. 

The  refractive  index  of  dipotassium  uranyl  nitrate  given  by  the  faces  (001) 
and  d  (101)  were  found  to  be  1.5422  for  light  vibrating  parallel  to  the  b  axis 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS. 


215 


and  1.5349  for  light  vibrating  in  the  ac  plane  26°  34§'  from  a  toward  c  in  the 
^* acute"  angle  jS. 

The  composition  was  investigated  by  igniting  to  K2UO4  and  by  washing 
out  the  K2SO4  from  sulphuric-acid  solution  precipitated  with  NH4OH  and 
weighing  the  resulting  UaOg  and  K2SO4. 


Theoretical. 

First. 

Second. 

K2U04 . . 
K2S04. . . 
U308.... 

p.ct. 
63.78 
47.09 
29.19 

p.ct. 
64.61 
46.85 
30.36 

p.ct. 
63.52 
47.03 
29.01 

The  best  crystals  were  obtained  by  cooling  solutions  supersaturated  1 
gram  in  100  c.c. 

MONOAMMONIUM   UrANYL  NiTRATB. 

/3  form  NH4U02(N03)3. 

This  salt  forms  from  solutions  containing  uranyl  nitrate  and  ammonium 
nitrate  at  room  temperature  if  the  acid-content  is  high  and  from  water  at 
higher  temperatures. 

System  trigonal;  axial  ratio  a  :c  =  I:  1.0027  (a  97°60.  The  forms  are 
prismatic  combinations  of  prism  a  (1120)  with  the  rhombohedron  r  (1101)  on 
the  end,  on  the  edges  of  which  occur  s  (1012). 


Theory. 

Steinmetz. 

W. 

r:r=1101  r'lOll  ... 
s:s  =0112  :  1102  ... 

81°  47' 
51°  19' 

81°  54' 
51°  30' 

82°    8' 
51°  36' 

The  column  headed  Theory  gives  the  values  for  a  substance  having  an  axial 
ratio  a  :  c  =  1: 1,  the  close  approximation  to  which  makes  this  a  remarkable 
case  and  probably  indicates  something  concerning  the  structure. 

Twins  were  observed  in  which  the  contact  plane  was  s  1 102  and  the  twin- 
ning axis,  the  axis  of  reference  to  which  s  was  parallel,  making  the  angle  be- 
tween the  two  unique  axes  119°54'  and  giving  the  crystal  the  appearance  _of  a 
flat  hemimorphic  orthorhombic  crystal.  The  angle  between  the  two  r  (1101) 
faces  was  calculated  to  be  21°32'  and  found  to  be  21°=t . 

Crystals  of  this  form  are  stable  in  dry  air,  but  begin  to  deliquesce  and 
change  to  a  light  yellow  chalky  mass  if  the  vapor-pressure  of  water  is  above 
9  mm.  Hg. 

Intense  pleochroism  was  observed  in  crystals  about  0.01  mm.  thick  on  a 
microscope  slide,  when  they  occurred  lying  on  a  prism  face,  the  light  vibrat- 
ing parallel  to  the  unique  axis  appearing  white,  i.  e.,  less  yellow  than  the 
mother-liquor  in  which  the  crystal  lay,  while  that  ordinary  ray  appeared  a 
deep  yellow. 

The  monopotassium  and  monoammonium  crystals  separate  from  the  same 
solution,  there  being  no  tendency  to  form  mixed  crystals. 

The  composition  of  the  crystals  was  checked  as  being  the  same  as  that 
given  by  Meyer  and  Wendel  by  igniting  to  the  oxide.  Theory,  59.22  per 
<;ent  found,  58.97,  and  58.86. 


216 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


Dl AMMONIUM  UrANTL  NiTRATB. 

a  form  (NH4)2U02(N03)42H20. 

This  phase  crystallizes  from  sHghtly  acid  solutions  of  uranyl  nitrate  con- 
taining a  large  excess  of  ammonium  nitrate.  Its  solubihty  increases  very 
rapidly  with  rising  temperature,  imtil  at  about  60°  C.  the  uranyl  nitrate  dis- 
solves out,  leaving  a  residue  of  ammonium  nitrate.  This  salt  crystalhzes 
very  readily  in  large  sulphur-yellow  perfect  crystals  of  5  or  10  grams  from  a 
volume  of  solution  that  only  gives  1  or  2  grams  of  monoammonium  salt  and 
crystalhzes  best  if  the  room  temperature  is  10°  to  15°.  The  fluorescence  is 
very  faint  at  20°  C,  but  increases  rapidly  below  0°,  becoming  stronger  than 
that  of  the  monoammonium  salt  at  liquid-air  temperatures. 

System  monocHnic  axial;  ratio  a:h:c  =  0.8419: 1  : 0.5594;  /3  94°55'.  The 
habitus  resembles  that  of  a  cube  with  octahedron,  the  forms  being  c  (001), 
a  (100),  6  (010),  and  o  (111).  The  faces  p  (110)  were  also  occasionally  observed, 
and  possibly  (211). 

No  cleavage  was  observed,  thus  increasing  the  resemblance  to  sulphur 
crystals.  However,  on  heating  rapidly,  the  crystals  fill  with  cracks,  and  con- 
sequently seeded  crystals  often  have  a  large  single  crack  more  or  less  parallel 
to  a  (100). 

Etch  figures  produced  by  resolution  in  a  crystal  in  the  mother-hquor  were 
found  once,  the  distinct  forms  being  on  h  (010),  with  two  rounded  faces  meet- 
ing in  a  fine  in  the  bottom  as  though  a  lens  had  been  pressed  in.  The  bottom 
edges  were  all  parallel  and  about  halfway  between  the  edges  of  h  (010)  and 
0  (111),  i.  e.,  parallel  to  (102). 

The  specific  gravity  was  found  to  be  2.777. 

When  these  crystals  are  heated  slowly  they  break  down  at  about  140°, 
giving  a  pasty  mass  full  of  bubbles,  which  clears  up  shghtly  at  220°,  but  does 
not  give  a  clear  solution  below  240°.  On  coohng,  bright  green  crystals  of  the 
monoammonium  salt  form  in  a  background  of  white  ammonium  nitrate. 

Crystals  of  this  phase  placed  over  sulphuric  acid  with  a  pressure  of  water- 
vapor  of  4  mm.  started  to  lose  water,  turning  to  a  whitish  powder,  and  con- 
tinued to  do  so  slowly  at  5  mm.,  although  then  they  do  not  start.  Placed 
over  sulphuric  acid  with  a  vapor-tension  of  11  mm.,  they  dehquesce  rapidly, 
soon  going  completely  into  solution. 

The  refractive  index  was  observed  in  two  different  directions,  using  natural 
faces.  First,  between  111  and  III  giving  the  fight  vibrating  in  the  ac  plane 
nearly  parallel  to  the  edge  olllrolll,  with  an  index  of  1.546,  and  that  at 
right  angles  to  the  ac  plane  as  1.639;  between  the  faces  6  010  and  o  111, 
giving  for_fight  appearing  on  h  to  vibrate  nearly  parallel  to  edge  between  b  (010) 
and  o'  111  as  1.508,  and  at  right  angles  to  that  1.619. 

The  composition  was  determined  by  ignition  to  U3O8,  which  gave  47.68 
and  47.62  per  cent  against  theoretical  47.58. 

URANYL  CHLORIDE. 

'Neither  the  monohydrate  UO2CI2H2O  described  by  de  Coninck^  as  being 
formed  by  evaporating  the  solution  prepared  by  precipitating  the  sulphate 
solution  nor  the  trihydrate,  which,  according  to  Mylius  and  Dietz,^  forms  from 

*  de  Coninck,  Comptes  Rendus,  148,  1769.     1909. 

»  Mylius  and  Dietz,  Ber.  d.  d.  Ch.  Ges.,  34,  2774.     1901. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS. 


217 


the  evaporation  of  the  solution  of  the  oxide  in  hydrochloric  acid,  were  suc- 
cessfully prepared  and  freed  from  the  sirupy  mother-Uquor  so  as  to  give  good 
fluorescence  spectra. 

Double  Chlorides. 

The  alkali  double  chlorides,  as  was  discovered  early  in  this  investigation  in 
the  case  of  the  ammonium  salt,  give  resolved  spectra  at  room  temperature. 
This  makes  the  group  quite  important.  The  four  double  salts  of  ammonium, 
potassium,  rubidium,  and  caesium  were  prepared.  Attempts  were  made  to 
prepare  the  double  salts  with  silver,  cadmium,  zinc,  and  calcium,  and  also 
hydrazine  and  hydroxylamine,  but  resulted  in  each  case  in  the  formation  of 
the  crystals  of  the  chloride  added,  in  a  sirup  or  mat  of  the  uranyl  chloride. 
The  silver  was  sealed  in  a  tube  with  a  strong  HCl  solution  as  solvent,  but 
although  remaining  white  did  not  dissolve  and  recrystalUze.  The  tetramethyl 
and  tetraethyl  ammonium  chlorides  described  by  Rimbach  were  not  made. 

The  alkah  double  chlorides  in  general  were  grown  by  evaporation  in  a  des- 
iccator in  presence  of  an  excess  of  HCl,  which  is  necessary  to  prevent  hydrol- 
ysis of  the  uranyl  chloride.  This  forces  back  the  solubiKty  of  the  alkah  salt, 
so  that  the  solutions  usually  contain  an  excess  of  uranyl  chloride.  The 
crystals,  if  allowed  to  stand  in  the  open  air,  readily  give  off  acid,  turning  the 
color  of  any  indicator  paper  on  which  they  are  placed  and  in  moist  atmosphere 
deliquesce  readily,  the  sirupy  uranyl  chloride  running  away  from  a  skeleton 

of  alkaU  chloride. 

Potassium  Uranyl  Chloride. 

K2U02C14-2H20. 

This  salt  was  described  by  de  la  Provostage^  as  occurring  in  hexagonal 
tables  on  c  (001)  bounded  by  o  (111),  w  (iTT),  m  (110),  m  (110),  h  (010),  q  (021). 
The  crystals  measured  by  Rammelsberg  were  mostly  prismatic  along  the  a 
axis.  The  first  type  were  those  used  in  this  work,  although  crystals  tabular 
on  h  (010)  were  fairly  frequent. 


System  trichnic;  axial  ratio,  a:  6 :  c:  =  0.607 
7  =  91°18'. 


1  :  560.    a  =  80°41' ;  ^  =  77°42' ; 


K2UO2CI4.2H2O. 

(NH4)2U02Cl4.2H20. 

Calculated. 

de  la  Provostage. 

Rammelsberg. 

Grailich. 

W. 

m  :6  =  (110):(010)... 
M  :6=(1T0):(0T0)... 
H  :c  =  (110):(001)... 
&  :  c  =  (010)  :(001)... 
q  :  c  =  (012): (001)... 
0  :  c  =  (111) :(001) 

60°  28' 
61°  33' 
83°  48' 
99°  15' 
65°  21' 

60°  30' 
61°  10' 
83°  55' 

60°  52' 

60°30'± 

61°  0' 

60°  48' 
85°  26' 
99°  34' 
56°  22' 
59°  40' 
47°  4' 

83°    0' 

98°  53' 
55°  45' 

55°  30' 
60°  15' 
46°  55' 
81°    0' 
75°  20' 
46°    5' 
66°  45' 

w':c=  (Til): (001).  . 

o  :b=  ail): (010) .. . 

80°    0' 
75°  30' 

w'  :b=  (Til)  :(010)  ..  . 

w':  q=  (111): (012)... 

0  :Ai'=(lll):(T10)... 

m  :  c  =  (110)  :(001). .. 

46°  17' 
66°  33' 

76°    8' 



The  properties  of  the  crystals  were  similar  to  those  of  the  ammonium  salt, 
although  the  crystals  seemed  to  grow  larger  more  readily. 

1  de  la  Provostage,  Ann.  Chim.  Phys.  (3),  6,  165.     1842. 


218 


FLUORESCENCE    OF   THE    URANYL    SALTS. 


In  the  work  of  Jones  and  Strong/  it  was  found  that  the  absorption  bands 
persist  far  out  into  the  red,  only  the  intensity  decreases  with  such  rapidity 
that  great  depths  of  solution  were  required  to  show  them.  To  try  this  out 
in  the  case  of  the  resolved  spectra  of  the  chlorides,  thick  layers  were  built  up 
of  several  crystals  and  found  out  to  hold.  A  very  deep  crystal  was  grown  in 
a  glass  tube  ground  into  the  bottom  of  an  inverted  bottle-neck  which  held  the 
solution.     This  crystal,  which  was  3  cm.  thick,  was  never  tried. 

Another  investigation  which  was  never  finished  was  that  of  the  char- 
acter of  the  spectra  of  mixed  crystals,  of  which  potassium  ammonium  salt 
K-NH4-U02-Cl4*2H20  was  prepared  as  an  example. 

Ammonium  Uranyl  Chloride. 

(NH4)2U02Cl4-2H20. 

The  crystal  forms  of  this  salt  are  practically  identical  with  that  of  the 
potassium  salt,  as  shown  by  the  table  of  angles  under  that  salt.  Intense 
pleochroism  is  noticed  in  this  crystal  when  viewed  through  the  c  (001)  face 
if  the  crystal  is  about  1  mm.  thick.  The  Hght  vibrating  parallel  to  the 
b  (010)  edge  of  the  face,  i.  e.,  parallel  to  the  axis,  is  so  Httle  absorbed  as  to 
appear  white  and  is  also  least  refracted.  The  Hght  vibrating  nearly  parallel 
to  the  h  axis  is  strongly  absorbed  in  the  blue-violet  and  appears  deep  yellow 
even  in  these  crystals.  The  refractive  indices  parallel  to  a  and  nearly  parallel 
to  h  and  c  were  measured  on  prisms  cut  so  that  light  traveled  parallel  to  the 
c  face  and  at  right  angles  to  it.  It  happens  that  the  letters  of  the  refractive 
indices  correspond,_,to  the  axes  to  which  they  are  nearest. 


a 

b 

c 

X720. 
X580. 
X500. 

1.564r-1.566 
1.566-1.574 
1.576-1.581 

1.619 
1.633 

1.622 
1.637 
1.650 

The  absorption  is  so  great  parallel  to  b  that  the  value  for  X  500  could  not 
be  obtained. 

Rubidium  Uranyl  Chloride. 

Rb2U02Cl4-2H20. 

This  is  similar  to  the  potassium  and  ammonium  salts;  although  no  measure- 
ments were  taken,  the  crystals  could  not  be  distinguished,  except  by  knowing 
the  individual  crystals. 

CESIUM  Uranyl  Chloride. 

CS2UO2CI4. 

The  salt  was  crystallized  as  above  from  a  solution  containing  caesium  chlo- 
ride and  uranyl  chloride  and  presented  a  distinctly  different  appearance  from 
the  other  members  of  the  group.  This  is  accounted  for  by  the  composition, 
which,  according  to  Rimback,  Wells  and  Boltwood,^  is  the  anhydrous  chlo- 
ride instead  of  containing  2  molecules  of  water,  as  with  the  other  salts.  The 
crystals  were  elongated  rhombs  of  yellow  color,  showing  less  fluorescence  than 
the  other  salts.     Under  the  polarizing  microscope  they  showed  a  striking 

1  Jones  and  Strong,  Carnegie  Inst.  Wash.  Pub.  No.  130,  90. 

2  Wells  and  Boltwood,  Zeit.  Anorg.  Chem.,  10,  181.     1895. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS. 


219 


resemblance  to  gypsum,  possessing  the  ^'fish-tail"  twins  and  approximately 
the  same  angles  and  appearing  different  only  in  the  yellow  absorption.  The 
crystals  were  so  universally  twinned  that  the  interfacial  angles  could  not  be 
determined  certainly.  The  largest  face  was  b  (010),  with  the  two  prism  faces 
m  (110)  and  ^  (110),  and,  as  determined  by  measurement,  practically  all  the 
end  faces  were  d  (Oil),  r  (031),  s  (031),  although  these  usually  appeared  twice 
on  a  crystal,  and  other  faces  indicated  by  the  measurement  were  glll,a;(lll). 
System  triclinic. 


6:m  =  010:110  =  49°  7' 
6:iu  =  010:iro  =  50"'50' 
6:d  =  010:011  =  40°31' 
6:  r  =  010: 031  =67°  48' 
6:  8  =  010:021  =  57°  41' 


m:  3  =  110:111=43"  41' 
m:r  =  110: 031  =86°  49' 
M:r  =  110:031=44°  0' 
M:x  =  ri0:lll=75°24' 


The  refractive  index  was  determined  through  the  faces  h  (010)  and  fi  (110), 
the  more  deviated  ray  vibrating  at  an  angle  of  about  15°  from  the  prism  edge 
toward  the  a  axis. 


X720 

1.618 

1.692 

X580 

1.625 

1.695 

X500 

1.634 

1.714 

The  index  was  also  determined  through  the  faces  b  (010)  and  d  (Oil),  the 
less-deviated  ray  vibrating  parallel  to  this  prism  edge. 


X580  1.614 

X580  1.622 


Urantl  Sulphate. 
U02S04-3H20. 

This  salt  was  prepared  by  Cragwall,  presumably  as  the  trihydrate.  On 
recrystalhzation  of  Kahlbaum  material  two  forms  appeared,  a  yellow  opaque 
needle-mass  tending  to  replace  the  bright  green  fluorescent  grains.  The 
yellow  needles  became  more  numerous  on  adding  sulphuric  acid,  so  uranic 
oxide  was  added  to  saturation,  which  proved  to  be  in  excess  on  evaporation. 
The  bright  green  fluorescent  crystals  were  difficult  to  keep,  as  they  dried  out 
readily  in  the  air.  Microscopic  examination  of  the  Cragwall  preparation 
showed  needles  with  parallel  extinction  and  greater  absorption  and  greater 
index  the  long  way  of  the  crystals,  while  the  angle  of  the  optical  axes  was 
very  large  and  the  sign  positive. 

The  acid  sulphate,  H2U02(S04)25420,  was  reported  by  Wyrouboff.^ 

DOUBLE  URANYL  SULPHATES. 

The  double  sulphates  differ  from  the  previous  double  salts  in  the  occurrence 
of  the  sodium  salt.  The  potassium,  ammonium,  rubidium,  caesium,  and 
thallous  salts  were  also  prepared  by  Cragwall  in  the  form  of  powders  result- 
ing from  rapid  precipitation  by  cooling.  The  potassium  and  rubidium  salts 
especially  showed  very  strong  fluorescence,  the  sodium  and  ammonium  good 
fluorescence,  the  caesium  less,  and  the  thalhum  practically  none,  and  that  was 
not  resolved.  Rimbach^  describes  a  dipotassium  salt  which  was  not  pre- 
pared and  one  of  hydroxylamine  also. 

iWyrouboff,  Bull.  Soc.  fran.  min.  No.  32,351,  1909. 
2  Rimbach.  I.  c,  479. 


220 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


These  salts  were  all  prepared  by  crystallization  from  water  of  the  calculated 
quantities  of  the  two  single  salts.  Rimbach^  describes  the  potassium  ammo- 
nium and  rubidium  salts  as  having  each  2  molecules  of  water  of  crystaUization. 
On  the  other  hand,  de  Coninck^  describes  the  sodium  potassium  and  caesium 
salts  as  having  3  molecules  of  water,  while  the  ammonium  commonly  has  2, 
but  can  be  made  by  special  conditions  with  3  molecules. 

Potassium  Uranyl  Sulphate. 

K2U02(S04)22H20. 

This  salt  separates  readily  on  coohng  a  hot  saturated  solution  of  the  two 
salts  in  equimolecular  proportion.  This,  according  to  Rimbach,  gives  the 
dihydrate,  according  to  de  Coninck^  the  trihydrate.  The  salt  prepared  in  this 
way  is  a  fine  crystalhne  powder,  larger  masses  being  clusters  of  crystals.  A 
good  crystal  was  discovered  in  an  old  solution  of  known  strength.  They 
were  then  obtained  by  supersaturating  0.1  to  0.5  gram  of  salt  in  50  to  200  c.c. 
of  solution,  seeding,  and  allowing  the  tightly  stoppered  solution  to  stand  from 
3  to  6  months,  especially  in  the  fall,  when  the  room  temperature  gradually 
decreases.  The  crystals  tend  to  form  rosettes,  clusters  of  crystals  arising 
from  the  middle  of  the  basal  pinacoid.  The  smaller  crystals  are  tabular  on 
the  base;  the  larger  ones  have  large  prism  faces  made  up  really  of  repeated 
pyramids.  These  are  capped  by  the  unit  pyramid  with  brachydome  and 
basal  pinacoid. 

System  rhombic;  axial  ratio  a:h:  c  =  0.5889: 1 :  0.6253. 


calc. 


obs. 


b: 
c: 

m  = 
n  = 

0  = 

k-- 
1  = 
Q  = 

=  010 
=  001 
=  001 
=  001 
=  001 
=  001 

110 

101: 

201  = 
.011 
021- 
112  = 

=  32° 
=  43° 

1' 

18' 

32° 
43° 
62° 
30° 
49° 
30° 

13 
0 
3' 

c: 
r  • 

=  30° 

30' 

19' 
90' 

c: 

=  29° 

4' 

0' 

calc. 
c:p  =  001:lll=48°  2' 
c:  r  =  001: 332  =  59°  3' 
c:  s  =  001: 221  =  65°  47' 
c:  f  =001:331=73°  18' 
c:w  =  001:441  =  77°20' 


obs. 
48°  6' 
59°  30' 
64°  45' 
71°  52' 
77°  25' 


II  to  b. 

II  to  a. 

C 

II  to  c. 

X720... 
X580. . . 
X500... 

1.5610-1.5627 
1.5670-1.5705 
1.5785-1.5847 

1.5220 
1.5266 
1.5350 

1.5096 
1.5144 
1.5202 

No  pleochroism  was  observed.     Plane  of  axes  a  (100),  obtuse  bisectrix 
normal  to  base.     Double  refraction  +.     Cleavage  was  observed  on  the  base. 

Rubidium  Uranyl  Sulphate. 
Rb2U02(S04)42H20. 

The  rubidium  salt  was  more  fluorescent  than  the  potassium  salt  and  mor 
difficult  to  crystallize,  so  that  measurements  of  it  were  not  obtained.     It  is, 
however,  completely  isomorphous  with  the  potassium  salt.    The  composition, 
according  to  Rimbach,^  is  as  above,  with  2  molecules  of  water. 

1  Rimbach,  I.  c,  478. 

2de  Coninck,  Bull.  Acad.  Roy.  Belg.,  1904,  1171;  1905,  50,  94. 

« Ibid.,  1905,  50. 

*  Rimbach,  I.  c,  479. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  221 

CiESiuM  Urantl  Sulphate. 

CS2U02(S04)23H20. 

This  salt  is  so  insoluble  that  no  crystals  could  be  produced.  The  Cragwall 
product  recrystallized  showed  on  the  microscope-shde  square  plates  about 
10  M  in  length,  which  showed  a  negative  uniaxial  figure.  This  salt,  according 
to  de  Coninck,^  has  the  same  composition  which  he  finds  for  the  potassium 
salt,  that  is,  3H2O. 

Ammonium  Uranyl  Sulphate. 

(NH4)2U02(S04)22H20. 

This  salt  was  not  recrystallized,  but  showed  similar  characteristics  to  the 
potassium  salt.  When  recrystallized  it  gave  bundles  of  needles,  the  vibra- 
tions across  which  were  most  absorbed  and  most  refracted.  Rimbach  de- 
scribes the  salt  as  having  2  molecules  of  water.  The  crystals  were  foimd  to  be 
monocHnic  by  de  la  Provostaye.^ 

Sodium  Uranyl  Sulphate. 
Na2U02(S04)23H20. 

This  salt  is  described  by  de  Coninck  as  having  3  molecules  of  water,  which 
he  finds  also  in  the  potassium  salt.  This  salt  as  prepared  by  Cragwall  was 
not  recrystallized,  but  showed  under  the  microscope  one  optical  axis  and  the 
acute  bisectrix  with  positive  double  refraction.  It  is,  therefore,  presimiably 
triclinic,  as  the  acute  bisectrix  was  off  normal  in  both  directions. 

Thallous  Uranyl  Sulphate. 

Tl2U02(S04)23H20. 

This  salt  was  prepared  by  Cragwall  from  weighed  amounts  of  the  two  salts 
according  to  Kohn,^  who  found  the  salt  to  be  of  the  above  composition  with 
probably  3H2O.  The  crystal  description  by  Himmelbauer  in  the  same 
article  gives  the  system  as  rhombic,  the  symmetry  from  etch  figures  pyramidal. 
The  forms  are  the  three  pinacoids  with  pyramid  faces  at  the  corners  which 
were  too  small  to  measure.  He  observed  through  (100)  in  converged  polarized 
hght  the  plane  of  the  axes  for  red  and  blue,  at  right  angles  the  plane  of  the 
blue  being  that  of  the  a  and  c  axes;  for  green  nearly  uniaxial;  for  red  hght 
a  is  the  acute  bisectrix,  the  pleochroism  on  (100)  distinct,  parallel  to  c,  deep 
yellow;  parallel  6  yellowish  white,  but  no  noticeable  pleochroism  on  (010). 
Crystals  up  to  3  mm.  in  diameter  and  1  mm.  thick,  produced  by  slow  cooUng 
of  the  Cragwall  salt,  showed  the  axial  figure,  but  it  could  not  be  surely  seen 
to  agree  with  the  description,  due  to  the  intense  absorption  in  the  blue  and 
green.  The  figure  might  be  explained  by  anomalous  dispersion  due  to  the 
absorption  band. 

PHOSPHATES. 

Uranyl  phosphate  (HUO2PO4.3-2-H2O),  which  precipitates  from  uranyl  solu- 
tions on  adding  phosphates,  possesses  no  fluorescence.  If  it  is  dissolved 
in  an  excess  of  acid  it  gives  a  glass  or  sirup  with  a  brilliant  fluorescence  which 
can  not  be  resolved  beyond  the  bands.  The  sodium  double  salt  was  made 
by  adding  sodium  phosphate  to  produce  H2Na2C02(P04)2  to  the  uranyl 
phosphate  with  an  excess  of  water,  which  on  standing  and  evaporating  gave 

1  de  Coninck,  Bull.  Acad.  Roy.  Belg.,  1905,  94. 

2  de  la  Provostaye,  Ann.  Chim.  Phys.  (3),  5,  51.     1842. 

3  Kohn,  Z.  Anorg.  Chem.,  59,  111.     1908. 


222  FLUORESCENCE   OF  THE   URANYL   SALTS. 

a  fine  crystalline  mass  which  was  very  fluorescent.  The  spectrum  of  this  was 
studied.  The  potassium,  ammonium,  lithium,  and  calcium  salts  were  also 
prepared  and  seen  to  have  characteristic  line  spectra,  but  were  not  studied 
further.  The  mineral  autunite  is  a  basic  calcium  uranyl  phosphate  which 
Stokes^  says  shows  brilhant  fluorescence,  while  chalcohte,  the  analagous  copper 
compound,  has  none,  but  shows  the  same  absorption  bands  characteristic 
of  uranyl  compounds. 

CHROMATES. 

An  attempt  was  made  to  prepare  the  sodium  uranyl  chromate  described  by 
Rimbach,  which  resulted  in  a  brown  mass.  The  uranyl  chromate  U02Cr04- 
3H2O  (Orloff)2  from  UO3  and  CrOs  gave  yellow  needles  with  no  fluorescence. 
The  potassiimi  salt  from  K2Cr207  and  UO3  was  also  without  fluoresecence. 

FLUORIDES. 

Cragwall  prepared  the  uranous  and  uranyl  fluoride  from  UaOs  and  HF,  which 
showed  practically  no  fluorescence.  He  also  prepared  the  double  potassium 
salt  K3UO2F6  by  adding  KF  to  uranyl  nitrate  and  (NH4)3  UO2F5  by  dissolving 
(NH4)2  U2O7  in  HF.3  The  double  salts  showed  characteristic  spectra,  but  the 
fluorescence  was  very  weak. 

URANYL  lODATE. 

This  salt  was  prepared  from  sodium  iodate  and  uranyl  nitrate  by  Cragwall 
by  a  method  which,  according  to  Artmann,^  would  result  in  U02(I03)2H20  of 
the  rhombic  form.    This  showed  little  fluorescence. 

MISCELLANEOUS  INORGANIC  COMPOUNDS. 

An  attempt  was  made  to  produce  bromides  and  iodides  analogous  to  the 
chloride  salts  without  results,  due  to  decomposition  with  the  liberation  of 
bromine  and  iodine.  An  attempt  was  also  made  to  produce  molybdyl  and 
tungstyl  ammonium  chloride  double  salts  analogous  to  the  uranyl  salts  by 
heating  the  oxides  with  ammonium  chloride  and  hydrochloric  acid  in  sealed 
tubes,  which  in  some  cases  resulted  in  crystals,  which,  however,  showed  no 
fluorescence.  Uranic  acid  or  H2UO4  was  also  sealed  up  in  tubes  with  anhy- 
drous hquid  NH3,  CO2,  SO2,  and  HCl.  None  of  the  resulting  compounds 
were  soluble  or  fluorescent,  although  changes  took  place,  the  carbonate  being 
nearly  white,  the  sulphur-dioxide  tube  greenish,  due  to  reduction,  and  the 
ammonia  tube  reddish  like  the  diuranate. 

Of  the  uranates,  the  sodium  potassium  calcium  and  barium  were  made,  none 
of  which  showed  fluorescence,  the  first  two  being  golden  yellow  plates,  the 
latter  two  an  amorphous  greenish  mass. 

URANYL  ACETATES. 

The  anhydrous  uranyl  acetate  U02(C2H302)2  was. prepared  by  Cragwall 
according  to  Spath^  by  adding  acetic  anhydride  to  uranic  oxide.  This  latter 
took  up  some  water  and  became  partially  the  dihydrate.  On  recrystalHzing 
some  of  the  material  from  acetic-acid  solution,  small  clear  cubes  were  obtained 
which  appeared  to  contain  acetic  acid  of  crystallization. 

1  Stokes,  Phil.  Trans.  Roy.  Soc.  London,  142,  518.     1852. 

*  Orloff,  Chem.  Ztg.,  31,  375.     1907. 

3  H.  F.  Baker,  Chem.  Soc.  Jour.,  35,  763-769.     1879. 

■*  Artmann,  Z.  Anorg.  Chem.,  79,  327,     1913. 

"  Spath,  Monatsh.  J.  Ch.  33,  248.     1912. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  223 

Uranyl  Acetate  Dihydrate. 

U02(C2H302)22H20. 

This  salt  was  prepared  by  Cragwall  by  recrystallizing  the  anhydride  from 
water  solution.  There  was  also  a  stock  of  material  from  Kahlbaum  and  un- 
known sources.  In  an  attempt  to  recrystalhze  this  salt  in  large,  clear  crystals 
much  difficulty  was  met,  as  it  usually  fills  with  cracks  as  it  grows.  The  best 
material,  having  as  much  as  4  mm.  cube  of  clear  material,  was  obtained  by 
supersaturating  2  grams  in  200  c.c.  and  allowing  a  month  or  two  to  crystalUze. 
The  crystal  properties  were  found  to  be  similar  to  those  described  by  Schabus,* 
the  system  being  rhombic,  with  an  axial  ratio  of  0.7817: 1:0.3551,  with  the 
forms  m  (110),  a  (100),  r  (101),  n  (120),  and  h  (010).  The  prism  zone  is  very 
much  striated,  affording  a  continuous  procession  of  reflections  in  the  gonio- 
meter. Schabus  finds  cleavage  on  m,  a,  6,  c,  which  accounts  for  their  extreme 
friabihty.  Zehenter^  finds  the  specific  gravity  to  be  2.893.  The  refractive 
index  was  determined  through  the  dome  as  being  1.490  for  light  vibrating 
parallel  to  the  c  axis  and  1.521  parallel  to  h. 

The  uranyl  acetate  trihydrate,  which,  according  to  Schabus,  forms  below 
10°  C,  was  not  prepared.  It  crystaUizes  in  the  tetragonal  system  with  an 
axial  ratio  of  a :  c  =  1 : 1.4054. 

DOUBLE  URANYL  ACETATES. 

The  sodium  salt  occurs  in  the  acetates  as  well  as  the  sulphates  and  is  the 
only  uranyl  salt  crystallizing  in  the  regular  system.  The  ammonium  and 
potassium  salts  seem  to  be  isomorphous,  in  spite  of  the  fact  that  the  potassium 
salt  is  said  to  contain  1  molecule  of  water  and  the  ammonium  salt  to  be  anhy- 
drous. The  silver  salt,  which  contains  1  molecule  of  water,  is  apparently 
isomorphous  and  the  rubidium  salt  was  found  to  have  a  similar  axial  ratio,  as 
usual  very  near  that  of  the  ammonium  salt.  The  similarity  of  axial  ratio 
to  that  of  the  uranyl  nitrate  trihydrate  suggests  that  these  salts  form  a  group 
that  might  well  be  studied  further.  The  csesium  salt  could  not  be  obtained, 
the  uranyl  dihydrate  crystallizing  out  and  leaving  the  caesium  acetate  in 
solution.  The  two  hydrates  of  lithium  uranyl  acetate  fully  described  by 
Wyrouboff^  as  being  monoclinic  were  attempted,  but  only  the  room-tempera- 
ture form  was  obtained.  The  double  salts  of  uranyl  acetate  with  bivalent 
acetates  were  in  general  prepared  by  dissolving  the  oxide  or  carbonate  of  the 
second  metal  in  acetic  acid  in  excess,  adding  uranyl  acetate  in  calculated 
amount,  with  water  enough  for  complete  solution,  and  allowing  to  crystallize 
by  slow  evaporation.  Difficulties  were  encountered  in  the  preparation  of 
some  of  the  salts,  such  as  the  calcium  salt,  which  Rammelsberg  also  could  not 
obtain,  as  described  by  Weselsky,^  which  was  finally  prepared  by  Weselsky 
method  of  precipitation  with  calcium  carbonate  and  solution  of  the  precipitate 
in  acetic  acid.  The  barium  salt  was  finally  prepared  by  this  method.  The 
cadmium  was  never  prepared  at  all;  at  least,  no  specimen  that  gave  anything 
but  the  uranyl-acetate  spectrum.  An  attempt  to  produce  a  mercuric  acetate 
also  failed. 

1  Schabus,  Prieschr.  Wien,  207.     1855. 

2  Zehenter,  Monats  f.  Ch.,  21,  235.     1900. 

3  Wyrouboff,  Bull.  Soc.  fran.  min.,  8,  115-122.     1885. 
*  Weselsky,  J.  Prakt.  Chem.,  75,  55.     1858. 


224  FLUORESCENCE    OF   THE    URANYL   SALTS. 

The  double  acetates  as  a  group  were  studied  by  Wertheim/ Schabus,^ 
Grailich,^  Weselsky/  and  Rammelsberg.^  The  acetate  group  in  general  show 
much  less  intense  fluorescence,  tending  to  be  of  a  dull  yellow  color. 

The  uranyl  double  acetates  with  bivalent  metals  may  be  divided  into  two 
classes — the  normal  and  the  abnormal.  The  group  HU02(C2H302)33H20 
appears  to  act  as  a  unit  in  forming  crystals.  In  the  alkali  double  salts  the 
water  of  crystallization  seems  to  be  lacking,  at  least  in  the  well-confirmed 
cases  of  the  sodium  and  ammonium  salts.  The  case  of  the  manganese,  cad- 
mium, and  lead  double  salts  seem  also  to  be  an  exception,  but  with  the  other 
double  acetates  the  ratio  of  uranium  acetate  to  bivalent  acetate  seems  to  be 
2  to  1.  The  water  of  crystalUzation  is  variously  given  from  7,  which  was 
found  uniformly  by  Rammelsberg,  to  8  by  Wertheim  and  10  by  Grailich. 
Since  the  water  is  likely  to  run  high,  due  to  occluded  mother-Hquor,  and  is 
such  a  small  per  cent  of  the  total  weight,  it  is  not  unreasonable  to  assume  that 
these  really  are  all  hexahydrates.  The  manganese,  when  satisfying  this 
valence  ratio,  and  magnesium  salts  seem  also  to  have  2  molecules  of  water  to 
each  uranyl  radical.  In  the  case  of  the  triple  salts  this  requirement  is  exactly 
fulfilled,  each  valence  of  base  having  a  U02(C2H302)3H20  group  attached  to  it. 

In  the  case  of  the  manganese,  cadmium,  and  lead  salts,  this  radical  does 
not  seem  to  act,  but  simply  the  two  acetates  are  present  in  a  1  to  1  ratio.  The 
spectra  of  the  manganese  salt  was  like  that  of  the  other  double  acetates;  the 
cadmium  was  not  formed  or  else  gave  a  spectrum  like  that  of  the  single  ace- 
tate, and  the  lead  was  one  of  the  salts  which  showed  fluorescence  Unes  coinci- 
dent with  spark  lines,  so  that  no  generalization  can  be  made. 

Sodium  Uranyl  Acetate. 
NaU02(C2H302)3. 
This  well-known  salt  described  by  Grailich®  crystallizes  in  the  regular  system 
with  the  least  or  pentagonal  dodecahedral  symmetry.  It  is  usually  in  the 
form  of  tetrahedra,  yellow,  with  light  green  fluorescence.  Johnsen^  gives  the 
specific  gravity  as  2.562  and  the  refractive  index  as  1.5014.  Marback^  and 
Traube^  give  the  optical  rotation  as  1.48°.  ,The  best  crystals,  up  to  3  mm.  in 
thickness  by  8  mm.  diameter,  were  obtained  on  long  standing  of  slightly 
supersaturated  solutions.  Dr.  Nishikawa  tried  to  obtain  X-ray  diffraction 
patterns  with  these  crystals,  but  could  obtain  nothing. 

Potassium  Uranyl  Acetate. 

KU02(C2H302)3H20. 

This  salt  was  described  by  Wertheim^°  as  having  1  molecule  of  water,  which 
was  also  found  by  Schabus"  and  Rammelsberg.^^  A  recent  determination  by 

1  Wertheim,  Jour,  of  Prakt.  Chem.  29,  207-231.     1843. 

2  Schabus,  Best.  d.  Kystall  gest.  i.  chem.  Lab.  Erz  Prod.  Preischr,  Wien.     1855. 

3  Grailich,  Kryst  Opt.  Untersuchung.  Preisch.  Wien,  pp.  151-175.     1858. 
*  Weselsky,  Jour,  f .  Prakt.  Chem.,  75,  55-62.     1858. 

6  Rammelsberg,  Sitz.  ber.  Acad.  Wiss.  Berl.,  857-887,  1884;  Wied.  Ann.,  24,  293-318,  1885. 

6  Grailich,  Preisschr.  Wien,  151.     1858. 

'  Johnsen,  N.  Jahrbuch  of  Min.  B.  B.,  23,  259.     1907. 

8  Marback,  Pogg.  Ann.  d.  Phys.,  94,  422.     1855. 

8  Traube,  Liebisch  Grundries  der  Phys.  Kryst.,  327.     1896. 
1°  Wertheim,  J.  Prakt.  Chem.  29,  223.     1842. 
"  Schabus,  Sitz.  ber.  k.  Akad.  Wiss  Wien,  857.     1884. 
12  Rammelsberg,  Wied.  Ann.,  24,  293.     1885. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  225 

Zehenter^  gives  1/2  H2O.  Since  the  isomorphous  ammonium  salt  is  without 
water,  and  since  both  potassium  acetate  and  uranyl  acetate  are  hygroscopic 
and  the  salt  occurs  in  needles,  it  seems  likely  that  the  water  is  not  in  the 
crystals.  The  crystals  are  mostly  prism  and  pyramid  of  the  tetragonal  system, 
with  the  axial  ratio  a:c=  1:1.2831,  according  to  Schabus.  The  specific 
gravity  is  given  by  Zehenter  as  2.396.  The  best  crystals  were  obtained  by 
slow  cooUng,  the  tendency  being  to  form  needles.  It  was  prepared  by  dis- 
solving weighed  potassium  carbonate  in  an  excess  of  acetic  acid  and  adding  the 
required  amount  of  uranyl  acetate. 

Ammonium  Uranyl  Acetate. 

(NH4)U02(C2H302)3. 

This  salt  was  prepared  and  measured  by  Rammelsberg,^  who  found 
the  axial  ratio  1:1.4124  in  the  tetragonal  system  apparently  isomorphous 
with  the  potassium  salt.  GraiUch  and  Schrauf'  assigned  1  molecule  of  water 
to  this  salt,  but  Rammelsberg  denies  this.  Zehenter  gives  the  specific  gravity 
as  2.219.  This  was  prepared  by  Cragwall  by  crystalHzing  equal  molecular 
quantities  of  the  two  salts  together. 

Rubidium  Uranyl  Acetate. 

RbU02(C2H302)3.?H20. 

This  salt  was  prepared  by  crystalHzing  uranyl  acetate  in  calculated  amount 
with  rubidium  acetate  produced  by  evaporating  off  rubidium  chloride  several 
times  with  acetic  acid.  On  cooUng,  tetragonal  needles  separated  out,  but  on 
further  evaporation  the  uranyl  acetate  separated,  leaving  the  rubidium  acetate 
in  solution.  The  crystals  were  measured,  giving  an  angle  oim  =  (111): 
(110)  =  26°33',  which  corresponds  to  an  axial  ratio  of  a:  c  =  1: 1.4151. 

Silver  Uranyl  Acetate. 

AgU02(C2H302)3H20. 

This  salt  was  prepared  and  measured  by  Wertheim,  who  found  it  tetra- 
gonal, with  an  axial  ratio  of  1.5385.  He  assigns  1  molecule  of  water  of 
crystallization,  which  seems  doubtful.  This  was  prepared  from  calculated 
quantities  of  uranyl  acetate  and  silver  acetate  dissolved  in  aqueous  acetic 
acid.  If  left  in  the  light  the  solution  decomposes,  which  resulted  in  many 
of  the  crystals  being  covered  with  a  black  coating  of  silver.  These  crystals 
are  more  incUned  to  be  granular. 

Lithium  Uranyl  Acetates. 
LiU02(C2H302)33H20. 

This  is  given  by  Wyrouboff*  as  crystallizing  in  the  monoclinic  system  with 
the  axial  ratio  a:h:c  =  1.2647: 1: 1.5849;  ^  =  99°53'.  It  forms  readily  on 
crystallization  of  water  solution  of  the  two  acetates,  but  does  not  give  very 
good  crystals.  The  other  hydrate,  LiU02(C2H302)35H20,  with  forms  below 
15°  was  not  obtained.  The  solution  was  made  by  adding  to  weighed  hthium 
carbonate  which  had  been  treated  with  an  excess  of  acetic  acid  a  calculated 
amount  of  uranyl  acetate.  This  was  put  in  a  desiccator  over  dehydrated 
potassium  acetate  in  an  unheated  room  in  winter,  but  the  5H2O  phase  was 
not  found. 

1  Zehenter,  Monatsh.  f.  Chem.,  21,  235.     1900. 

2  Rammelsberg,  Sitz.  ber.  Acad.  Wiss.  Berl.     1859. 

3  Schrauf,  Sitz.  ber.  d.  Acad.  Wiss.  Wien,  41,  779.     1860. 
*  Wyrouboff,  Bull.  Soc.  fran.  Min.,  8,  115.     1885. 


226  FLUORESCENCE   OF  THE   URANYL   SALTS. 

Magitosium  Urantl  Acetates. 

Mg(U02.  (C2H302)3)27H20. 

This  salt  was  found  by  Wertheim/  who  assigned  it  8  H2O,  examined  by 
GraiUch,^  who  gave  IOH2O,  and  finally  given  7H2O  by  Rammelsberg.^  It 
was  found  to  crystallize  in  the  rhombic  system  with  the  axial  ratio  0.8944 : 
1 :  0.9923,  one  of  the  series  of  five  isomorphous  salts  Mg,  Fe,  Co,  Ni,  and  Zn. 
Lang*  gives  negative  double  refraction,  axes  in  (001)  plane,  bisectrix  a  2E  = 
100°,  and  p<  v.  This  salt  was  prepared  by  evaporation  of  a  solution  made  by 
adding  to  a  weighed  sample  of  MgO  an  excess  of  acetic  acid  and  the  cal- 
culated amount  of  uranyl  acetate.  The  crystals  grow  fairly  large,  up  to  5  mm. 
with  some  readiness. 

Mg(U02(C2H302)3)2l2H20. 

This  hydrate,  according  to  Ranmielsberg,^  forms  at  low  temperatures  in 
large,  rapidly  weathering  crystals  with  an  axial  ratio  of  0.7667:1:0.5082. 
According  to  Grailich  and  Lang,^  the  double  refraction  is  negative,  the  axes 
in  a  (100),  bisectric  c,  2E=13°  for  red  and  10.5°  for  blue.  The  fluorescence 
is  given  as  very  strong  emerald  green.  This  hydrate  was  not  obtained  for 
examination. 

Calcium  Uranyl  Acetate. 
Ca(U02(C2H302)3)28H20. 

The  salt  was  prepared  by  Weselsky  and  examined  by  GraiHch.^  Rammels- 
berg  attempted  to  repeat  this  determination  and  could  not  obtain  good 
crystals.  Graihch  found  them  to  be  of  the  rhombic  system,  with  an  axial 
ratio  of  0.9798:1:0.3865,  with  many  faces.  Lang^  found  interior  twins. 
Grailich  found  no  pleochroism,  but  greenish-blue  fluorescence.  This  salt  was 
produced  according  to  Weselsky's  precipitation  method  after  the  addition 
method  had  failed. 

Strontium  Uranyl  Acetate. 
Sr(U02(C2H302)3)26?H20. 

This  salt  was  also  prepared  by  Weselsky  and  could  not  be  obtained  by 
Ranamelsberg.  It  was  measured  by  Grailich,  who  reports  it  as  being  in  the 
tetragonal  system,  with  an  axial  ratio  of  1 : 0.3887.  No  trouble  was  found 
in  producing  it  from  strontium  carbonate,  acetic  acid,  and  uranyl  acetate. 

Barium  Uranyl  Acetate. 
Ba(U02(C2H302)3)26H20. 

This  salt  was  first  produced  by  Wertheim  and^  later  described  by  Rammels- 
berg,^"  both  of  whom  found  6  molecules  of  water,  but  neither  of  whom  obtained 
crystals  good  enough  to  measure.  The  Weselsky  method  was  also  necessary 
to  produce  this  compound,  the  first  attempt  giving  only  the  uranyl  acetate 
crystals. 

1  Wertheim,  I.  c,  225.  e  Lang,  Sitz.  ber  d.  Akad.  Wis8  Wien,  108,  iia,  562.   1899. 

*  Grailich,  I.  c,  152.  ^QraUich,  I.  c,  159. 
«Rammel8berg,Wied.Ann.,24,303.  *  Lang,  L  c,  107. 

*  Lang,  I.  c,  107.  9  Wertheim,  l.  c,  230. 

^  Rammelsberg,  Sitz.  ber.,  869.  1°  Rammelsberg,  I.  c,  300. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  227 

Zixc  Uranyl  Acetate. 
Zn  (U02(C2H802)3)2  7H2O. 
This  salt  was  prepared  by  Weselsky^  and  examined  by  Grailich.^  Rammels- 
berg  found  the  axial  ratio  to  be  0.8749 : 1 : 0.9493  in  the  rhombic  system. 
Graihch  and  Lang^  found  negative  double  refraction  with  the  axes  in  c  (001), 
bisectrix  h.  The  color,  according  to  Grailich,  is  yellow  with  weak  pleuchroism; 
fluorescence  is  faint  greenish.  This  salt  from  zinc  oxide,  acetic  acid,  and 
uranyl  acetate  crystalUzed  after  some  trouble  in  rhombic  plates  with  Httle 
fluorescence.  The  uranyl  acetate  sometimes  separated  without  the  formation 
of  the  double  salt.     This  belongs  to  the  isomorphous  magnesium  group. 

Cadmium  Uranyl  Acetate. 
Cd.U02.(C2H302)46H20. 

These  crystals  were  made  by  Weselsky*  and  examined  by  Grailich,  who 
found  an  axial  ratio  of  0.6289 : 1 : 0.3904  in  the  rhombic  system.  These 
crystals  were  also  analyzed  by  Rammelsberg,^  who  found  that  the  composition 
did  not  correspond  to  that  of  the  zinc  salt,  but  had  a  1  to  1  ratio  of  bivalent 
cadmium  to  uranium,  thus  making  it  hke  manganese  and  lead.  These  crystals 
could  not  be  prepared,  nothing  but  the  uranyl  acetate  spectra  being  obtained. 

Manganese  Uranyl  Acetate. 
MnU02(C2H302)46H20. 

These  crystals,  prepared  by  Weselsky^  and  examined  by  Grailich,^  were 
found  to  have  the  axial  ratio  of  0.6330 : 1 : 0.3942  in  the  rhombic  system  by 
Rammelsberg.  The  optical  properties,  according  to  Lang,  are  double  re- 
fraction, negative,  plane  of  the  axes  a  (100),  bisectric  c,  2E  =  31°,  with  a 
yellow  color.  When  prepared  by  evaporation  of  an  acetic-acid  solution  of 
manganese  carbonate  and  uranyl  acetate,  small  yellow  crystals  were  obtained. 

Mn  [(UO2)  (C2H302)3]2  I2H2O. 

These  efflorescing  crystals,  obtained  by  Rammelsberg^  from  the  1 : 1  solu- 
tion of  the  acetates  while  warm,  which  solution  later  deposited  the  other 
hydrate,  is  isomorphous  with  the  magnesium  dodecahydrate.  Rammelsberg 
found  it  to  be  of  the  rhombic  system,  with  the  axial  ratio  of  0.7536:1:0.4957. 

Lead  Uranyl  Acetate. 

PbU02(C2H302)44H20. 

This  salt  was  obtained  by  Wertheim®  and  later  by  Rammelsberg,^''  who  gave 
it  the  above  formula,  which  puts  it  in  the  1 : 1  class  with  cadmium  and  man- 
ganese. The  crystals  are  very  readily  formed  as  needles  of  any  length — the 
greater  the  supersaturation  the  longer  the  needles.  Some  fairly  compact 
plates  were  obtained  as  a  second  crop  from  a  highly  supersaturated  solution. 
These  were  made  from  lead  acetate  and  uranyl  acetate  in  weighed  proportions. 

TRIPLE  ACETATES. 

These  salts  were  discovered  by  Rammelsberg"  in  an  attempt  to  get  a  copper 
uranyl. double  acetate  and  are  found  when  sodium  acetate  is  present  with  the 
bivalent  metals,  magnesium,  manganese,  iron,  nickel,  cobalt,  copper,  zinc, 

1  Weselsky,  .  Ic,  58.  '  Rammelsberg,  I.  c,  887.  »  Wertheim,  /.  c,  227. 

2  Grailich,  I.  c,  171.  *  Weselsky,  I.  c,  59.  *°  Rammelsberg,  Wied.  Ann.,  314. 
« Lang,  I.  c,  51.                        ^  Granich,  I.  c,  175.                     ^^  Ibid.,  315. 

*  Weselsky,  I.  c.,61.  ^  Rammelsberg,  I.  c,  872. 


228  FLUORESCENCE    OF  THE   URANYL   SALTS. 

and  cadmium  salts  being  reported.  They  are  characterized  by  a  temperature 
dimorphism  being  above  a  given  temperature,  trigonal,  and  below  that  mono- 
cHnic  twins  and  pseudotrigonal.  They  all  have  the  same  type  formula  de- 
rived from  the  monovalent  uraniacetic  acid  HU02(C2H302)33H20,  which 
takes  on  in  this  case  1  atom  each  of  monovalent  metal  (sodium  in  all  cases 
studied)  and  1  bivalent  metal.  These  formula  may  also  be  written  NaOH+R 
(OH)2-f3U02(OH)2  +  9HC2H3O2,  which  would  explain  the  exact  relation 
between  the  number  of  acetic  radicals  and  molecules  of  water  of  crystallization. 
This  series  was  studied  by  Erb^  and  by  Wyrouboff  .^  The  temperature  change 
was  studied  by  Schwarz.^  This  group  is  characterized  by  the  pseudotrigonal 
appearance  of  a  large  basal  pinacoid,  six-sided,  due  to  rhombohedron  faces 
which  are  uneven,  due  to  twinning.  They  are  readily  distinguished  from 
uranyl  acetate  or  the  metallic  acetate  or  uranyl  double  acetates  by  this  char- 
acteristic shape.  They  do,  however,  resemble  the  sodium  uranyl  acetate 
considerably  if  it  has  imeven  faces,  due  to  the  varying  composition  of  the 
solution  as  it  crystalUzes.  Under  the  crossed  nicols,  however,  there  is  no 
question,  the  very  characteristic  twinning  surfaces  showing  unmistakably. 
Sodium  Magnesium  Uranyl  Acetate. 
NaMg[(U02(C2H302)3  SHzOzJs. 
These  crystals,  according  to  Wyrouboff,^  are  simply  monocHnic  if  grown 
below  15°  C.,  but  as  the  temperature  rises  the  twins  become  more  numerous, 
until  at  50°  the  whole  crystal  becomes  trigonal.  This  process  then  reverses 
on  cooling.  Erb^  describes  them  as  sulphur-yellow  crystals  which  weather 
readily.  The  axial  ratio  has  not  been  determined  closely  because  of  the 
twinning.  These  crystals  were  grown  better  by  slow  evaporation  than  by  slow 
or  rapid  cooUng  of  supersaturated  solutions. 

Sodium  Zinc  Uranyl  Acetate. 
NaZn[(U02(C2H302)  SmO]z. 

These  crystals  were  produced  by  Erb,  who  did  not  obtain  sufficient  measure- 
ments to  calculate  the  axial  ratio.  The  temperature  of  conversion  was  found 
by  Schwarz  to  be  95°.  These  crystals  were  made  by  adding  to  zinc  oxide  an 
excess  of  acetic  acid,  sodium  uranyl  acetate,  and  uranyl  acetate  in  calculated 
proportions.  These  crystals  were  identified  by  the  twins,  as  shown  by 
polarization.  They  were  found  to  weather  fairly  rapidly,  even  in  moist 
summer  weather. 

Sodium  Cadmium  Uranyl  Acetate. 

NaCa[U02(C2H302)3  SHzOla. 
These  crystals,  prepared  and  measured  by  Wyrouboff,*  have  the  axial  ratio 
a:  6:  c  =  0.5162: 1:0.9798;  i8  =  90°9';  plane  of  the  axes  normal  to  h  (010) 
and  nearly  parallel  to  a  (100) ;  positive  bisectrix  parallel  to  6,  with  large  axial 
angle.  The  change  to  a  uniaxial  figure  does  not  take  place  until  nearly  200°, 
at  which    temperature  the   crystals   effloresce. 

1  Erb,  N.  Jahr,  of  Min.  B.  B.,  6,  121-147.     1888-89. 

2  WjrroubofT,  Bull.  Soc.  fran.  Min.  24,  93-104.     1901. 

3  Schwarz,  Beitr.  Z.  Kenntn.  d.  umkehrbaren  Umwandlungen  polymorpher  Korper.  Preisschr 

d.  Univ.  Gottingen.     1892. 
*  WjTouboff,  I.  c,  104. 
5  Erb,  l.  c,  126. 
<>  Wyrouboff.  I.  c,  103. 


CHEMISTRY   OF   FLUORESCING   URANYL   SALTS.  229 

Sodium  Copper  Uranyl  Acetate. 
Na  Cu[U02(C2H302)3  SHjO],. 

This  was  the  first  salt  of  this  series  to  be  discovered  by  Rammelsberg.  The 
axial  ratio  is  given  by  Wyrouboff  as  a:  6:  c  =  0.5354:l :  0.9950;  i3  =  89°55'. 
The  double  refraction  is  weakly  positive,  plane  of  the  axes  normal  to  b  (010) ; 
the  bisectrix  50°  from  c  axis  in  the  acute  angle  through  the  face  c  (001); 
2E  =  90°  50';  dispersion  weak,  r  <  v.  According  to  Wyrouboff,  it  only 
becomes  uniaxial  at  140°,  while  Schwarz  finds  the  conversion-point  at  93.8°. 
This  salt  was  prepared  from  cupric  hydroxide,  acetic  acid,  uranyl  acetate,  and 
sodium  acetate  in  weighed  amounts.  On  slow  evaporation,  large,  clear 
crystals,  though  not  free  from  twins,  were  obtained,  some  being  1  cm.  in  dia- 
meter and  2  mm.  thick.     These  were  sealed  in  glass  to  prevent  efflorescence. 

An  attempt  was  made  to  produce  the  cobalt  salt  of  this  group,  but  it  was  not 
very  successful.  The  manganese,  iron,  and  nickel  were  not  tried.  The  last  salt 
was  studied  rather  completely  by  Johnsen^  in  an  investigation  of  twinning. 

Uranyl  Oxalate. 
UOjCC^OO  3H2O. 

This  salt  was  described  by  Pehgot  and  Ebelmen^  and  later  by  Zimmerman.' 
This  is  an  apparently  amorphous  powder  produced  by  adding  oxaUc  acid  to 
the  neutral  nitrate,  which  shows  under  the  microscope  small  grains  with 
brilUant  polarization  colors  and  an  extinction  angle  with  the  long  side  of  the 
crystals  of  13°.  A  specimen  of  this  was  prepared  by  Cragwall  and  some 
material  was  also  purified  this  way. 

DOUBLE  URANYL  OXALATE. 

The  double  salts  seem  to  be  formed  fairly  readily,  the  potassium  salt  being 
described  by  Ebelmen^  and  the  ammonium  salt  by  de  la  Provostage^  and  by 
Rammelsberg.^  Wyrouboff^  makes  a  comprehensive  review,  giving  the 
following: 

K2  U02(C204)2  3H2O  monoclinic. 

(NH4)2  U02(C204)2  2H2O  rhombic. 

Cs2 1102(0204)2  2H2O  rhombic  isomorphous  with  above. 

TI2  UO2  (0204)2  2H2O  rhombic  isomorphous  with  above. 

Naa  UO2  (€204)2  6H2O  tricHnic. 

(NH4)4  UO2  (€204)3  monoclinic. 

TI4  UO2  (€204)3  monoclinic  isomorphous  with  above. 

Ko  UO2  (€204)4  IOH2O  tricUnic. 

None  of  these  salts  were  tried. 

Uranyl  Tartrate. 

U0204H406.4H20. 

This  salt  was  prepared  by  Cragwall  by  the  method  of  Peligot^  from  uranyl 
hydroxide  U02(OH)2  from  the  ignition  of  uranyl  nitrate  and  tartaric  acid. 

1  Johnsen,  N.  Jahrb.  Min.  B.  B.,  23,  259.     1907. 

2  Peligot  and  Ebelmen,  Liebig.  Ann.  Chem.  43,  282,  287.     1842. 
'  Zimmerman,  Liebig.  Ann.  Chem.,  232,  300.     1886. 

4  Ebelmen,  Ann.  Chim.  Phys.  (3),  5,  200.     1842. 

^  de  la  Provostage,  ibid.,  49. 

*  Rammelsberg,  Handbuch  d.  Krystall.  Chem.,  264.     1855. 

'  Wyrouboff,  Bull.  Soc.  Fran.  Min.,  32,  352.     1909. 

»  Pehgot,  Liebig  Ann.  Chem.,  56,  231.     1845. 


230  FLUORESCENCE   OF  THE   URANYL   SALTS. 

This  was  recrystallized  from  water  and  left  microscopic  plates  with  wide  black 
edges,  as  on  a  crystal  lying  on  b  (010)  and  bounded  by  m  (110)  and  c  (001),  or 
else  having  a  very  high  index,  a  low  double  refraction,  and  straight  hyper- 
bolas, as  from  a  tipped  uniaxial  crystal  or  near  an  optic  axis. 

DOUBLE  URANYL  TARTRATES. 

The  tartrates  are  exceedingly  soluble,  and  hkely  to  result  in  gums  on 
drying,  which  do  not  crystalhze.  The  existence  of  a  sodium  double  salt  in 
solution  is  indicated  by  the  work  of  Grossman^  and  Loeb  on  the  effect  of  heavy 
metals  on  the  rotation  of  tartaric  acid.  The  potassium  double  salt  is  de- 
scribed by  Frisch^  and  the  antimonyl  salt  by  Pehgot  (see  uranyl  tartrate), 
but  none  of  the  salts  show  fluorescence,  so  they  were  not  taken  up  further. 
The  corresponding  molybdyl  and  tungstyl  compounds  were  attempted,  since 
the  oxides  are  soluble  in  tartaric  acid,  but  only  thick  gums  which  did  not 
crystallize  or  fluoresce  were  obtained. 

Potassium  Uranyl  Tartrate. 

K2U02(C4H406)2. 

This  salt,  described  by  Frisch,  was  prepared  by  Cragwall  by  adding  uranyl 
nitrate  to  potassium  tartrate  and  washing  free  from  nitrates.  Since  Frisch 
produced  his  material  by  dissolving  precipitated  uranyl  hydroxide  in  acid 
potassium  tartrate  (Weinstein)  and  found  that  it  could  not  be  crystalUzed  by 
drying,  but  was  precipitated  by  alcohol,  it  seems  probable  that  the  material 
which  Cragwall  obtained  on  washing  was  simply  the  acid  potassium  tartrate 
itself.  Examination  for  fluorescence  and  under  the  microscope  indicated 
this. 

Antimonyl  Uranyl  Tartrate. 
U02.(SbO.C4H406)2  4H20. 

This  is  produced,  according  to  Pehgot,  by  adding  uranyl  nitrate  solution  to 
potassium  antimonyl  tartrate  solution.  Cragwall  washed  the  precipitate  free 
from  nitrates.  The  resulting  material  appeared  to  be  amorphous  and  showed 
no  fluorescence.  In  this  case  both  basic  radicals  are  commonly  in  the  complex 
anion,  so  that  it  is  difficult  to  decide  which  comes  first. 

Potassium  Uranyl  Propionate. 

K  U02(C2H602)3. 

Rimbach^  examined  the  potassium  and  ammonium  double  salts  with  pro- 
pionic acid  and  the  potassium  double  salt  with  butyric  and  valerianic  acids. 
These  crystalhze  in  tetrahedra,  according  to  Sachs,^  but  were  not  attempted 
for  this  work. 

1  Grossman  and  Loeb,  Z.  Phys.  Chem.,  72,  93.     1910. 

2  Frisch,  J.  Prakt.  Chem.  97,  281.     1866. 

3  Rimbach,  Ber.,  37,  484.     1904. 
*  Sachs,  Ber.  37,  484.     1904. 


APPENDIX  2. 

ON  PHOSPHOROSCOPES. 

The  uranium  salts  have  exhibited  under  photo-excitation  a  type  of  phos- 
phorescence which  persists  but  a  few  thousandths  of  a  second,  while  under 
cathodo-excitation  the  type  endures  for  several  minutes.  It  was  necessary 
to  devise  two  phosphoroscopes  of  entirely  different  design  to  measure  the  two 
types  of  phosphorescence.  The  choice  of  a  suitable  phosphoroscope  is  a 
matter  of  great  importance;  hence,  a  brief  summary  of  the  types  of  phosphoro- 
scopes which  have  been  employed  since  the  time  of  the  great  pioneer  student 
of  phosphorescence,  E.  Becquerel,  follows.  Among  the  considerations  which 
present  themselves  when  the  construction  of  a  phosphoroscope  is  contemplated 
are  the  quantity  of  phosphorescent  material  available,  the  total  time  of  decay, 
the  temperature  at  which  the  specimen  is  to  be  studied,  the  nature  of  the  ex- 
citation (e.  g.,  photo-,  ultra-violet,  cathode  rays,  etc.),  the  ease  with  which 
saturation  is  obtained,  and  the  initial  brightness  of  the  specimen.  The 
phosphoroscopes  which  have  been  constructed  can  be  divided  into  three 
classes : 

Type  1. — The  specimen  is  periodically  excited  and  periodically  viewed  at  a 
later  phase. 

Type  2. — The  specimen  is  continuously  excited  and  continuously  viewed  at 
a  later  phase. 

Type  3. — The  specimen  is  excited  for  a  measured  interval  of  time  and  the 
intensity  measured  at  a  later  time.  This  method  is  apphcable  to  the  slowest 
types  of  decay. 

Machines  which  may  be  classified  as  belonging  to  type  1  must  operate  at 
such  speeds  that  no  flicker  is  noticeable;  hence  the  weakest  intensity  measured 
must  fall  within  a  total  time  of  decay  of  one-sixteenth  of  a  second.  Many 
natural  crystals,  under  photo-excita- 
tion, present  very  interesting  phos- 
phorescence processes  which  appar- 
ently cease  in  less  than  this  time. 
The  very  first  steps  in  the  long-time 
decays  of  such  substances  as  the 
natural  and  artificial  sulphides  may 
be  studied  with  the  aid  of  a  phosphoro- 
scope belonging  to  type  1.  E.  Bec- 
querel^ devised,  among  other  forms,  a 
phosphoroscope  of  the  intermittently 
excited  type.  The  specimen  was 
mounted  between  two  parallel  disks 
and  was  alternately  illuminated  and 
observed  through  properly  adjusted  ^^^-  ^• 

openings  in  the  disks.  Figure  1  shows  two  such  disks,  each  having  four 
open  sectors,  mounted  on  the  same  axis  but  in  (different  phase.  Bec- 
querel caused  the  exciting  fight  to  pass  into  the  translucent  crystal  through 


1  E.  Becquerel,  Annales  de  Chimie  et  de  Physique  (3),  55,  p.  6.     1859. 


231 


232 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


the  rear  disk,  while  the  opaque  sector  prevented  the  light  from  coming  through 
the  phosphoroscope  to  the  eye.  As  the  disk  was  revolving  at  a  high  speed, 
the  Ught  was  quickly  stopped  from  passing  to  the  crystal  by  the  interposition 
of  an  opaque  sector  of  the  rear  disk.  A  small  fraction  of  a  second  later  the 
continued  rotation  brought  an  open  sector  of  the  front  disk  in  Hne  with  the 
crystal  and  the  eye,  thereby  allowing  the  phosphorescent  Hght  to  be  viewed 
on  a  dark  field.  The  rotating  parts  were  neatly  mounted  in  a  brass  drum 
and  driven  by  a  crank  through  a  system  of  gears.  With  such  a  type  of 
phosphoroscope  Becquerel  detected  the  glow  of  the  platino-cyanides  only 
0.003  of  a  second  after  excitation. 

It  is  evident  that  to  view  opaque  specimens,  the  excitation  can  not  be 
directly  behind  the  specimen;  hence  BecquereP  devised  a  phosphoroscope 
possessing  only  one  rotating  disk,  figure  2,  both  diagrams  with  three  openings, 
K,  L,  and  R,  arranged  120°  apart.  The  disk  revolved  on  a  vertical  axis 
between  two  fixed  openings,  180°  apart,  the  exciting  hght  from  X  passing  in 
through  one  of  these  two  openings  and  the  luminescent  hght  passing  out  from 
the  specimen  P,  upper  diagram,  through  the  other  opening  to  the  observer  0 
a  fraction  of  a  second  later.  In  figure  2  the  sector  is  shown,  in  elevation,  at 
such  a  position  that  the  open  sector  R  admits  exciting  Hght  to  P,  and  it  is 
evident  that  an  opaque  sector  is  at  that  time  to  be  found  at  S.  On  the  other 
hand,  when  S  is  opened  by  the  passage  of  an  open  sector,  the  open  sector  R 
has  passed  out  of  the  Une  XP  and  an  opaque  sector  is  interposed. 


Fig  .  2. 

E.  Wiedmann^  devised  a  phosphoroscope  consisting  essentially  of  a  hollow 
brass  drum  fitted  with  a  collimator  and  lens  and  revolving  disk  for  the  ad- 
mission of  the  exciting  hght.  The  exciting  hght  passed  intermittently  through 
the  open  sectors  of  a  sectored  disk  and  the  specimen,  which  was  mounted 
within  the  drum,  was  thus  intermittently  excited.  For  the  purpose  of  view- 
ing opaque  specimens  and  hquids  at  a  later  phase,  the  revolving  disk  carried 
on  the  periphery  a  band  with  open  sectors  for  excitation;  thus  the  path  of  the 
phosphorescent  hght  was  at  right  angles  to  that  of  the  exciting  hght.  Wiede- 
mann constructed  driving-gears  with  a  ratio  of  1,000  :1  and  hence  obtained  a 
rotary  speed  as  great  as  140  revolutions  per  second.  Either  the  unassisted 
eye  or  a  spectrometer  was  employed  to  view  the  phosphorescence.     Stray 

1  E.  Becquerel,  Annales  de  Chimie  et  de  Physique  (3),  v.  55,  p.  80.     1859. 

2  E.  Wiedmann,  Wiedmann's  Annalen,  vol.  34,  p.  446.     1888, 


ON   PHOSPHOROSCOPES. 


233 


I  ight,  always  a  menace  in  phosphorescent  studies  where  photo-excitation  is 
used,  was  present,  and  Wiedemann  appreciated  the  necessity  of  devising  some 
addition  to  his  apparatus  for  the  purpose  of  eUminating  it.  He  favored  the 
addition  of  another  revolving  sector,  similar  to  and  coaxial  with  the  first, 
having  openings  in  phase  with  it,  and  mounted  between  the  first  sector  and  the 
lens.  When  it  is  considered  that  the  intensity  of  the  undispersed  phosphor- 
escence is  from  1/100  to  1/1,000,000  that  of  the  exciting  light,  it  is  evident 
that  the  introduction  of  a  small  per  cent  of  the  exciting  hght  into  the  field  of 
the  phosphorescence  completely  aborts  any  attempt  at  quantitative  measure- 
ments. 


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FiQ.  3. 

E.  Merritt^  devised  a  phosphoroscope  of  the  first  type  in  which  the  phos- 
phorescent surface  P  (see  fig.  3)  was  illuminated  periodically  by  the  passage 
of  hght  from  a  spark  S  through  an  opening  through  a  revolving  disk  00', 
The  phosphorescence  could  be  observed  at  the  desired  later  time  by  changing 
the  phase,  while  the  machine  is  turning,  of  the  mirror  M  relative  to  the 
opening  0.  This  was  accomplished  in  a  unique  manner  by  means  of  the  rod 
L,  which  engages  a  hollow  sleeve  R  having  a  spiral  slot  cut  in  it.  A  pin 
capable  of  sliding  in  this  slot  and  attached  to  the  opposite  end  of  the  same 
inner  shaft  as  the  mirror  M,  is  moved  into  different  phases  with  the  disk  00' y 
which  is  mounted  on  the  outside  shaft.  This  outer  shaft  is  driven  by  a  belt 
and  pulley  and  is  keyed  to  the  sleeve  R;  thus  the  drive  is  complete.  Rod  L 
does  not  rotate,  but  can  be  locked  at  any  desired  phase.  Reflection  of  the 
phosphorescence,  then,  occurs  at  M,  a  simple  photometer  being  employed  to 
view  the  hght.  On  the  revolving  shaft  was  mounted  a  worm-gear  for  record- 
ing the  number  of  revolutions  per  minute.  With  this  form  of  phosphoroscope 
the  curves  of  decay  of  many  substances  were  traced  from  zero  time  up  to 
0.06  second. 

In  the  preceding  phosphoroscopes  the  source  of  hght  has  not  been  inter- 
mittent, but  the  periodic  interruption  of  the  beam  of  exciting  light  has  pro- 
duced the  effect  of  intermittent  excitation  on  the  specimen.  Another  group 
of  instruments  belonging  to  this  type  employs  an  intermittent  discharge  from 
condenser,  induction  coil,  or  transformer,  as  in  the  spark  phosphoroscope  of 

^  E.  Merritt,  Nichols  and  Merritt,  Studies  in  Luminescence,  Carnegie  Inst.  Wash.  Pub.  No. 
162,  p.  109.     1912. 


234 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


Laborde,^  which  included  a  rotating  pattern  to  hide  the  specimen  from  the 
observer  during  excitation  by  the  spark  from  an  induction  coil,  and  later 
uncover  the  specimen. 

Wm.  Crookes/  in  his  study  of  the  cathode  phosphorescence  of  yttria,  noted 
that  the  color  at  the  beginning  of  decay  was  different  from  that  observed  after 
the  decay  had  continued  for  a  short  period,  and  accordingly  devised  a  phos- 
phoroscope  to  study  this  change.  Figure  4  serves  to  show  that  it  was  of  the 
sectored-disk  form  and  driven  by  cord  and  pulley.  At  a  convenient  distance 
was  located  an  induction  coil  whose  primary  circuit  was  alternately  made  and 
broken  by  a  commutator  near  the  end  of  the  revolving  shaft  C.  The  brushes 
could  be  so  shifted  as  to  cause  the  excitation  of  the  phosphorescent  substance 
P  when  an  opaque  sector  passed  between  P  and  the  eye.  It  was  possible  to 
change  the  period  of  decay  by  changing  the  speed  or  by  changing  the  phase  of 
the  brushes  relative  to  the  edge  of  the  sector.  The  phosphorescent  substance 
was  mounted  in  a  convenient  form  of  cathode-ray  tube  and  excited  by  the  dis- 
charge from  the  secondary  of  the  coil.  With  the  aid  of  the  spectrometer, 
Crookes  discovered  that  different  lines  appeared  in  the  spectrum  of  the 
phosphorescent  yttrium  after  0.000875  second  than  at  0.0035  second. 


Fig.  4. 

Ph.  Lenard^  devised  a  phosphoroscope  which  differs  from  the  preceding 
forms,  since  no  revolving  disk  is  employed.  To  hide  the  specimen  from  view 
during  excitation  he  used  the  motion  of  a  screen  mounted  on  the  plunger  of  a 
Ruhmkorff  mercury  interrupter.  The  frequency  of  the  interrupter  was  de- 
termined by  that  of  the  spring  fork  on  which  it  was  balanced;  hence  change 
in  the  period  between  excitation  and  observation  was  accomplished  by  chang- 
ing forks.  The  discharge  of  a  condenser  in  parallel  with  secondary  circuit 
of  the  coil  was  thus  timed  bj^  the  interruptions  of  the  primary  circuit  to  occur 
while  the  vibrating  screen  was  in  front  of  the  specimen. 

De  Watteville'^  constructed  a  machine  similar  in  principle  to  that  of  Laborde 
and  Crookes  (see  fig.  5) .     The  specimen,  together  with  the  spark,  was  mounted 


^  Laborde,  Comptes  Rendus,  vol.  68,  p.  1576. 

2  Crookes,  Proceedings  of  the  Royal  Society,  vol.  42,  p.  111. 

2  Ph.  Lenard,  Wiedmann's  Annalen,  46,  p.  637. 

*  De  Watteville,  Comptes  Rendus,  142,  p.  1078. 


1887. 


ON   PHOSPHOROSCOPES. 


235 


in  the  box  K  and  was  visible  to  the  observer,  except  when  the  two  arms  of  the 
rotating  disk  D  intercepted  the  phosphorescent  hght.  At  such  times  one  of 
the  points,  P  or  P',  completed  the  circuit  from  B  through  A  to  i^,  allowing  the 
discharge  of  the  condenser  C  to  excite  the  specimen  at  K;  the  condenser  had 
been  previously  charged  by  coil  S.  Twice  a  revolution,  then,  the  specimen 
was  excited  and  observed. 


FiQ.  5. 

Nichols  and  Howes,^  to  study  the  phosphorescence  of  the  uranyl  salts,  de- 
vised a  phosphoroscope  of  considerable  precision.  Except  for  the  work  of 
Nichols  and  Merritt,  Trowbridge,  Ives,  and  a  few  others,  the  previously 
mentioned  students  of  phosphorescence  have  been  content  to  measure  the 
intensity  at  two  or  three  periods  of  decay,  but  the  above-mentioned  investi- 
gators have  taken  many  observations  on  one  substance  and  estabhshed  curves 
of  decay  for  each  substance  studied.  For  such  measurements,  refinements  for 
precluding  measureable  stray  light  and  for  accurately  measuring  the  time 
intervals  and  for  maintaining  constant  speed  are  a  necessity.  The  synchrono- 
phosphorosope  (see  fig.  6)  was  so  named  because  it  employs  the  principle  of  a 
sectored  disk  mounted  on  the  axle  of  a  synchronous  motor  A.  C.  This  motor 
was  raised  to  synchronous  speed  by  the  direct-current  motor  D.  C.  The 
transformer  TT  was  attached  to  the  same  alternating-current  terminals  as 
was  the  A.  C.  motor;  hence  the  discharge  of  the  condenser  occurred  as  many 
times  per  second  as  the  number  of  wave-crests,  i.  e,,  120.  There  were  four 
opaque  sectors  and  four  open  sectors  in  the  disk  WW,  and  since  the  four-pole 
machine  turned  at  a  speed  of  30  revolutions  per  second,  there  were  120  echpses 

*  Nichols  and  Howes,  Science,  n.  s.,  vol.  43,  p.  937.     1916. 


236 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


per  second.  By  means  of  a  small  set-screw  the  disk  could  be  clamped  at 
various  positions  on  the  shaft,  corresponding  to  various  times  in  the  decay 
process.  Without  the  star-wheel  SS  the  discharge  of  the  condenser  KK 
produced  an  exciting  spark  at  E,  which,  with  the  aid  of  a  revolving  mirror,  was 
found  to  consist  of  a  pilot-spark,  followed  by  five  or  six  smaller  sparks;  hence 
the  zinc  star-wheel  SS  was  mounted  on  the  shaft  to  reduce  the  discharge  to 
one  spark.  By  experimenting  with  small  and  large  capacities  it  was  found 
that  resonance  must  be  recognized,  and  the  proper  amount  of  capacity  to 
produce  a  regular,  strong  spark  was  finally  discovered.  The  measurements 
of  time  were  read  with  the  aid  of  the  hght  yielded  by  the  exciting  spark  by 
noting  the  position  of  the  edge  of  the  sectors  on  a  protractor  mounted  rigidly 
in  front  of  the  machine.  The  range  of  times  accurately  measureable  include 
those  from  0.0001  to  0.0040  second  by  0.0001-second  steps.  The  photometer, 
spectro-photometer,  camera,  and  spectrograph  have  been  successfully  used 
with  this  instrument. 


1  o 


'9 


L- 


©E© 


^^z::r^_-ZJ3_: 


Fig.  6. 

In  their  prehminary  study  of  the  cathodo-phosphorescence  of  the  rare 
earths,  Nichols,  Wick,  and  Wilber^  employed  a  phosphoroscope  with  a  disk 
mounted  on  the  shaft  of  a  motor.  The  primary  of  an  induction  coil  was 
interrupted  by  a  plunger  attached  to  a  crank  on  the  shaft  of  the  motor.  The 
plunger,  once  in  a  revolution,  dipped  into  the  mercury  cistern,  while  the 
opaque  portion  of  the  disk  hid  the  specimen  from  view,  and  as  a  result  the 
specimen  was  excited  by  the  discharge  of  the  secondary  coil  through  a  cathode- 
ray  tube,  much  after  the  manner  of  Crookes's  device. 

The  change  in  time  between  excitation  and  observation  was  accomplished 
by  changing  the  speed  of  the  motor,  and  an  anmaeter  in  the  field  circuit  was 
cahbrated  to  measure  the  angular  velocity.  It  is  evident  that  with  only  one 
excitation  per  revolution  only  one  open  sector  could  be  used. 

The  second  type  of  phosphoroscope  includes  those  instruments  by  means 
of  which  the  specimen  is  constantly  excited  and  constantly  viewed  at  a  later 
time.  Such  a  form  had  its  origin  with  E.  Becquerel.^  This  form  was  used  for 
lecture  demonstrations  by  Tyndall.^     In  its  simplest  form  it  consists  of  a 


1  Nichols,  Wick,  and  Wilber,  Physical  Review  (2),  vol.  14,  1919. 
'  Becquerel,  E.,  Annales  de  Chimie  et  de  Physique  (3),  vol.  62,  p.  5. 
»  Tyndall,  see  Lewis  Wright,  "Light,"  p.  152.     London,  1882. 


1861. 


ON   PHOSPHOROSCOPES. 


237 


drum  (see  fig.  7)  whose  periphery  P  is  covered  with  a  phosphorescent  sub- 
stance, provided  with  a  source  of  excitation  S  mounted  in  a  box  A,  and  driven 
by  belt  BB  and  pulley.  The  viewing  coUimator  or  photometer  is  indicated 
atE. 

Kester^  employed  a  device  of  this  type,  together  with  spectrometers  and 
radiometer,  to  study  the  relation  of  intensity  of  excitation  to  that  of  phos- 
phorescence. 


Fig.  7. 

Waggoner^  mounted  on  a  vertical  shaft  an  iron  drum  45  cm.  in  diameter. 
This  mass,  being  considerable,  acted  as  a  balance  on  the  irregularities  of  the 
motor  speed.  The  exciting  spark  was  so  mounted  that  it  could  be  moved 
about  the  drum,  thus  enabling  the  observer  to  measure  the  brightness  at 
various  times  after  the  spark  ceased.  The  periphery  was  painted,  as  before, 
with  the  phosphorescent  substance.  The  revolutions  of  the  drum  were  auto- 
matically recorded  on  a  chronograph.  With  this  device  the  spectrum  of  early 
phosphorescence  was  studied  with  the  aid  of  the  spectrometer  and  decay 
curves  of  the  total  visible  radiation  were  taken. 

Nichols  and  Howes,^  in  the  study  of  the  phosphorescence  of  calcite,  em- 
ployed this  type  with  a  drum  of  8.0  cm.  diameter  (see  fig.  8).  The  eye-piece 
E  was  arranged  at  180°  from  the  spark  A,  the  spark  thus  being  completely 
hidden  from  the  observer  by  the  opaque  drum  D.  Effective  screening  was 
added  to  prevent  stray  light  from  entering  either  face  of  the  Lummer-Brodhun 
cube  L,  B.  and  a  filter  F  was  interposed  between  the  comparison  lamp  C 


^  Kester,  Physical  Review  (1),  vol.  9,  p.  164. 

2  Waggoner,  Carnegie  Inst.  Wash.  Pub.  No.  152,  p.  119. 

^  Nichols,  Howes,  and  Wilber,  Physical  Review  (2),  vol.  12,  p.  350. 


1918. 


238 


FLUORESCENCE   OF  THE   URANYL   SALTS. 


and  the  cube  to  produce  a  color  match  with  the  reddish  color  of  the  phos- 
phorescence. Although  the  angle  between  spark  and  observing  photometer 
remained  constantly  180°,  the  time  of  decay  could  be  varied  between  0.01 
second  and  3  or  4  seconds  by  changing  the  motor  field  or  by  throwing  in  a 

DISK      PHOSPHOROSCOPE. 


o 


--^ 


Fig.  8. 


Fig.  9. 


worm-gear  drive.  Two  features  were  added  to  make  the  device  more  useful. 
First,  the  phosphorescent  substance  was  never  painted  on  the  disk,  but  on 
brass  rings  which  fitted  neatly  on  the  disk;  second,  the  speeds  were  known  by 
reading  on  a  galvanometer  G  the  deflections  produced  by  a  current  induced 


ON   PHOSPHOROSCOPES. 


239 


by  a  disk  below  the  phosphorescent  disk,  but  on  the  same  shaft.  This  disk 
cut  the  field  between  two  electromagnets  M,  one  brush  B  on  the  rim,  the 
other,  B',  on  the  shaft  delivering  the  current  to  the  galvanometer.  The  con- 
stancy of  the  niagnetic  field  was  maintained  by  examining  the  readings  of  an 
ammeter  in  series  with  the  electromagnets  and  storage  cells,  and  precautions 
were  taken  to  eliminate  thermal  electromotive  forces  at  the  brushes.  In  the 
use  of  this  type  of  phosphoroscope,  as  well  as  the  first  type,  readings  of  in- 


Fig.  10. 

tensity  are  only  comparable  through  a  range  of  speeds  for  which  saturation  is 
obtained.  With  the  red  variety  of  calcite,  saturation  was  found  to  exist  with 
the  iron  spark  1  cm.  from  the  disk  for  all  speeds,  which  gave  more  than  0.02 
second  decay;  hence  measurements  in  which  the  time  interval  from  the  close 
of  excitation  to  observation  was  not  greater  than  0.02  second  were  rejected. 
To  use  this  instrument  with  greater  precision  it  is  necessary  to  take  account 
of  the  variations  in  the  spark.  For  this  purpose  an  auxihary  station,  with 
photometer  P  and  lamp  C2,  was  arranged  (fig.  9),  where  simultaneous  readings 
of  intensity  of  phosphorescence  were  taken  while  the  chief  observer,  with  aid 
of  the  spectrophotometer  H  and  lamp  Ci,  measured  the  intensity  of  the  phos- 
phorescence throughout  the  spectrum. 


240 


FLUORESCENCE    OF   THE   URANYL   SALTS. 


To  study  the  early  stages  of  the  cathodo-phosphorescence  of  calcite,  Nichols 
and  Howes^  devised  a  vacuum  phosphoroscope,  outUned  in  figure  10.  The 
phosphorescent  specimen  was  apphed  to  the  periphery  of  the  disk  P  and 
excited  by  means  of  the  cathode  discharge  from  K.  The  vacuum-tube  V  was 
fitted  to  the  ground  plate  N.  The  shaft  was  balanced  in  an  iron  tube  115  cm. 
in  length,  the  mercury  rising  from  the  iron  reservoir  C  to  the  barometric 
height.  The  shaft  was  driven  by  a  pulley,  cord,  and  variable-speed  motor, 
and  the  revolutions  were  recorded  by  the  commutating  device  at  the  bottom 
wired  to  the  chronograph.  Intensities  of  phosphorescence  were  measured 
with  the  aid  of  lamp  P,  photometer  bar  S,  and  Lummer-Brodhun  cube  T. 

The  third  type  of  phosphoroscope,  in  which  the  specimen  is  excited  for  a 
definite  time  and  viewed  at  varying  but  definite  times  after  excitation,  in- 
cludes the  form  used  by  Nichols  and  Merritt  in  their  extensive  studies^  of  the 
luminescence  of  sidot  blende. 


Fig.  11. 

The  specimen  was  mounted  diagonally  in  a  box  having  two  openings  with 
shutters,  one  to  admit  excitation,  the  other  to  allow  the  luminescence  to  be 
viewed  after  excitation.  The  eye  of  the  observer  was  thus  protected  from  the 
briUiant  luminescence  during  excitation,  but  was  able  to  view  the  phosphor- 
escence with  no  fatigue  when  the  shutter  of  the  luminescence  window  opened. 
The  time  when,  the  phosphorescence  intensity  became  equal  to  that  of  the 
comparison  field  was  recorded  on  the  chronograph  by  means  of  a  key  in  the 

^  Nichols,  Howes,  and  Wilber,  I.  c. 

*  Nichols  and  Merritt,  Carnegie  Inst.  Wash.  Pub.  No.  152,  p.  41. 


ON   PHOSPHOROSCOPES.  241 

hand  of  the  observer.  A  series  of  such  comparisons,  together  with  the  initial 
time,  formed  a  series  of  points  for  a  decay  curve.  It  is  clear  that  such  a 
device  is  only  suitable  for  the  study  of  decay  which  endures  for  several  minutes. 

E.  H.  Kennard^  devised  a  phosphoroscope  of  this  type  with  shutters  actuated 
by  the  magnetic  release  of  phosphor-bronze  springs.  Three  shutters  {Si,  S2, 
S3,  of  fig.  11)  were  used.  Si  to  admit  exciting  hght  from  the  mercury  arc  A 
to  the  specimen  P,  S2  and  >S3  to  limit  the  time  during  which  the  phosphorescence 
was  allowed  to  produce  photo-electric  action  on  the  cell  C.  The  latter  adapta- 
tion to  phosphorescence  work  is  unique.  In  his  prehminary  work  the  times 
between  opening  and  closing  of  shutters  were  determined  from  the  known 
curve  of  a  ballistic  galvanometer,  the  passage  of  a  shutter  opening  and  closing 
shunts  which  allowed  a  definite  quantity  of  electricity  to  pass  into  the  gal- 
vanometer. In  his  later  work  the  shutters  were  magnetically  released  by  the 
swing  of  a  seconds  pendulum  across  mercury  cups  set  at  convenient  positions 
along  the  path  of  the  bob.  The  photo-electric  current,  for  low  intensities,  is 
proportional  to  the  intensity  of  phosphorescence  and  was  measured  by  a 
quadrant  electrometer. 

It  is  to  be  inferred  from  the  preceding  summary  on  phosphoroscopes  that 
there  may  be  no  single  machine  which  is  well  adapted  to  the  study  of  a  par- 
ticular phosphorescent  specimen  under  investigation.  As  in  the  study  of 
phosphorescence  in  the  past,  the  investigator  has  often  devised  one  or  more 
machines  for  the  study  of  the  various  types  of  phosphorescence;  so  in  the 
future  the  machine  must  be  adapted  to  the  behavior  of  the  specimen.  Then, 
too,  the  precision  with  which  the  time  of  observation  is  desired  makes  it 
necessary  that  the  modern  phosphoroscope  be  equipped  with  an  accurate  and 
if  possible  a  direct-reading  speed  register.  The  plotting  of  decay  curves  by 
Nichols  and  Merritt,  Trowbridge,  Ives,  and  others  made  it  imperative  that 
both  times  and  excitations  be  well  known.  The  lack  of  constancy  of  excita- 
tion has  been  recognized  and  observations  corrected.  The  importance  of 
obtaining  the  same  degree  of  saturation  before  decay  begins  is  paramount  if 
results  are  to  be  considered  comparable.  In  the  use  of  the  continuously 
excited  type  the  importance  of  this  factor  becomes  evident.  The  use  of  the 
interrupted  excitation  type  for  eclipses  of  16  or  less  a  second  should  be  entirely 
avoided,  because  of  the  behavior  of  the  eye  when  flicker  is  noticeable.  The 
human  eye  should  not  be  fatigued  beyond  instant  recovery  during  the  process 
of  observing  decay,  neither  should  it  be  dark-adapted  before  beginning  a  set 
of  observations.  The  necessity  of  adequate  screening  is  of  great  importance 
when  it  is  considered  that  luminescence  radiation  is  several  thousand  times 
less  than  the  photo-excitation  of  approximately  the  same  wave-length.  Stray 
luminescence  may  add  to  the  selected  portion  of  the  luminescence  beam  and 
produce  errors.  These  factors  are  fundamental  considerations  for  the  future 
student  of  phosphorescence. 

1  Kennard,  Physical  Review  (2),  vol.  4,  p.  278.     1914. 


8      4  7  f)  8 


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Fluorescence  of  the 
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Fluorescence  of  the 
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